Since depression is all about an imbalance of chemicals* inside your body, it makes sense that you're more prone to depression when your body isn't operating at full power. You're already behind, since you went through the delivery process. Any way it happens, it's a stress on your body. You're probably sleep-deprived before the baby's even on the outside, since the last few weeks of pregnancy are tough to sleep through (leg cramps, back pain, strange dreams, etc.). And that's not even considering how fatigued you are just from the pregnancy. Add on to that the fluids you lost during delivery and the sleep you're not getting now that the baby's here, and it's a real recipe for physical unwellness.
What that all means is that you have to be proactive about taking care of yourself physically. If at all possible, get your supplies and support all set up before you have the baby. If not, well, every little bit you can do helps.
Drink water. This is the single most important thing you can do for your health in the first few days post-partum. You need water to replenish yourself from the hard work of delivery and all the fluids you lost during the process. In addition, drinking lots of water will help flush out the pregnancy swelling, which will make it easier for you to get around and feel better about your body. (It won't do anything about the creepy feeling of all your organs going back into place, unfortunately.)
When I was leaving the hospital after having my first son, the doctor told me to drink a gallon of water a day for the first three weeks. He said it would help my body rid itself of toxins and get back to normal more quickly. Aiming for a gallon meant I'd get half a gallon, and if I drank a full gallon it wouldn't hurt me.
One stellar suggestion I've heard is to set up a few nursing/feeding stations around your living space. They should be comfortable places to sit and nurse or bottle-feed, and they should have all the things you'll need right within reach for you, including a bottle of water (plus a phone, remote control, magazine or book you can read one-handed, chapstick, etc.). Eery time you sit down to feed your baby, make sure you drink 8-12 ounces of water. By the end of the day, you'll have gotten what you need.
If you have a helper there, one great thing to occupy them is to put them in charge of keeping track of your water intake for the day and bringing you water when you need it.
Keep taking your prenatals. You probably need your prenatal vitamins more post-partum than you do during pregnancy to replace all the vitamins and minerals you lost with the baby and everything else. Vitamin deficiency can cause fatigue, problems sleeping, anxiety, depression, and all sorts of other things. So keep taking the prenates to ward off problems, especially since prescription prenatal vitamins can be cheaper through your health insurance plan than over-the-counter multivitamins are.
Keep taking your Omega 3s. I can't emphasize this enough. There's tons of research indicating the mental health benefits of taking Omega 3s. (The only problem right now is deciding whether to take fish oil or flax seed oil. I can't advise one way or the other at this point, since the research seems to be conflicting and muddled. I still take flax seed oil every day.) Omega 3s fill up your seratonin receptors to give you a feeling of wellness. If you don't have enough Omega 3 in your body, you'll crave sweets and carbs to hit those seratonin receptors, but that just starts a bad cycle. Because of the way we produce our food now (grain-fed farmed animals, for example) it's more difficult to get adequate levels of Omega 3s just from a healthy diet, so supplementation is critical, especially when you've just had a baby.
Lay off the diet products. Just as Omega 3s soothe your seratonin receptors, aspartame taxes your seratonin receptors, which makes you feel more hungry. Kind of a nasty trick, isn't it, that you've been drinking diet soda and it's just making you feel more hungry? People report headaches and irritability with consumption of aspartame, so if you're sensitive to it you could be feeling bad for no good reason. Since you're drinking at least half a gallon of water a day, you don't really need the extra fluids. If you need the caffeine, drink real coffee. If you need the fizz, mix your own "soda" with fruit juice and seltzer. (My favorite is white cranberry juice and seltzer. It's tart, and when you spill it down your shirt or on the baby's head it doesn't leave a stain.) If all else fails, drink a little bit of regular soda. The corn syrup in it is awful for you, but it's better than aspartame, and we have no idea what aspartame does through breastmilk to a baby.
Eat as well as you can. That doesn't mean truffles, Brie, and caviar, with a split of Cristal. That means 5 servings of vegetables a day, plus plenty of protein. Getting enough vegetables will keep your digestive system running smoothly, feed your cells, help you lose babyweight, and help you fight off illness. Protein is important to keep your energy level up. In addition, lack of protein sometimes masks itself as a craving for sugar. Sugar cravings can be just that, but often they indicate lack of liquids or protein. (So when you crave sugar, first drink a glass of water. Then eat some protein. If the craving is still there in 10 minutes, go ahead and eat the sweet thing.)
Having problems getting in the 5 servings of vegetables? Try doing green smoothies, with a huge handful of raw greens (spinach and kale are particularly great in this), some frozen fruit, and whatever liquid you want to thin it (fruit juice, water, milk, coconut milk, kefir, etc.), and blend until smooth. Extra bonus: You can drink it one-handed.
Get outside in the sunshine. It's that simple. If it's sunny, go outside for 15 minutes and expose some of your skin to the light, even if it's really cold. If you absolutely can't go outside, or there's no sun where you live (Hello to my Scandinavian and Alaskan readers!), consider investing in a light box to help keep your body stocked up on healthy light. If you're having insomnia or sleep schedule problems, you can also reset your system this way by going out in the sun first thing in the morning.
Do some exercise every day. Most women are cleared to go back to exercising at 6 weeks, but even before then you should be able to go outside and walk around slowly for 20 minutes at a time (listen to your body and don't overdo it!). Once 6 weeks hits, make sure you do some walking every day with your baby.
Another great mom-friendly exercise is T-Tapp, an exercise method you do at home with the DVD that takes 15 minutes a day and requires no special equipment except cross-training shoes. I do T-Tapp and find that it helps me sleep better, increases my mood and energy level, and gives me increased focus throughout the day. It's safe for people of all sizes and fitness levels (challenges even gym rats, but literally anyone can start it and feel benefits), and builds your muscular and lymphatic systems up from the inside. Here's a concise explanation of what T-Tapp does. If you're interested in starting out with T-Tapp but don't know how to start, Summer wrote the best getting-started primer I can imagine right here. (Summer's the one who got me started with T-Tapp, and I'll always be thankful to her for mentioning it on her blog.) T-Tapp also has mood-stabilizing properties if you do it several times a week or every day.
Maximize your sleep opportunities. You're not going to get 8 hours in a row when your baby is a few months old. You're just not, unless your baby is one of those apocryphal babies who sleeps through the night at a super-early age. It happens occasionally, but not to the majority of us. So that means you need to maximize the time your baby does let you sleep.
One plan is to ask your partner, if you have one, to do one feeding at night, so you can sleep through that waking. Of course, that only works if your partner won't wake you in the process of getting up with the baby. And if you're nursing and you have to get up and pump then anyway, it doesn't really make much sense as a strategy to get more sleep, since up pumping isn't sleeping through anything.
Another way to get more sleep, if you're nursing, is to ask someone to show you how to nurse lying on your side. Then decide to lie down every time you nurse during the day. You can latch the baby on and fall asleep (the nursing hormones will probably put you to sleep anyway if you're lying down), then sleep while the baby nurses, and if the baby sleeps after nursing you get that time to nap, too.
If you have helpers who are willing to come hold the baby for you, take advantage of that to nap. You may not be able to relax if the baby is in the same house or apartment with you, so let your helper take the baby out for a walk. The fresh air will be good for the baby, and you'll be able to sleep better without hearing baby noises.
If you find that you have the time to sleep, but can't sleep because of anxiety or stress, first make sure your Omega 3 intake is good. If it is, then consider adding a calcium and magnesium supplement. Take it 20 minutes before you go to bed, and see if that helps you relax any. If you're not already doing T-Tapp, it also helps people sleep better.
Keep your baby as close as you want to. You carried your baby for months inside you, never separate. All of a sudden, you are two entities instead of one. But you still need to be considered as a unit. If you're having feeding problems, it's a problem for both of you. The same with sleeping, bonding, and health problems. Hormonally, you're still connected, so most mothers without PPD feel better when their babies are close to them physically for the first several months, at least. (In my experience, I felt strange when my sons were away from me until right about the time that they could crawl away from me. I've heard the same thing from other mothers, and I don't think that's coincidence.)
All this is to say that you should hug and cuddle your baby as much as you want to. You know there's no way to "spoil" a baby by giving it too much physical closeness, but it will also help you physically and emotionally to keep your baby as close as you want to. If you're feeling stressed, you may want to get out of the house for a little bit without your baby, but it also may be helpful to strap your baby on with a sling, Bjorn, wrap, Ergo, etc., and go outside with your baby. Go walk around, wander the aisles of the grocery store, have a cup of coffee at a cafe, or go visit a friend. Getting a "break" from the normal routine doesn't necessarily mean separating from your baby, and if you're one of those women who feels discomfort at being separated from her baby, you're better off keeping your baby with you.
The newborn phase is so short in the scope of things, that there's no need to worry about independence issues (for either of you) at this point.
Get a massage whenever possible. If you have the financial ability to get a massage every so often, you can help maintain your health by getting one. Massage will help move toxins out of your body and stimulate the lymph and immune systems. It can also be an antidote, ironically enough, to the feeling of being "touched out" that many new mothers have. All day we're touched by our children, who want something from us, and then at night we're touched by our partners, who want something from us. It's surprisingly liberating to be touched by someone who doesn't want anything out of the touching except to increase our health and well-being.
If you can't afford a professional massage, your partner will probably be willing to give you one if you ask. Of course, this may make you feel even more "touched out," but if your partner does a good job the health benefits will be worth it.
Next installment: Taking care of yourself emotionally.
* After reading some of the comments, I realized that this is sloppy writing. Depression is a result of complex interactions that we don't understand completely yet, but we do know that there's an element of brain chemistry and/or hormones involved. Depression is sometimes an appropriate response to a crappy situation, but that doesn't mean it's good for you to be depressed, or for your baby to have a depressed mother.