If you aren't, start taking your prenatal again, or an over the counter version. The extra vitamins are great for women in general during their reproductive years. Other than that, it's been said, diet and exercise. I have chronic depression, it's a chemical imbalance and I can either live with it and control it the best I can or take meds for the rest of my life. I hate to take medication so I have learned to deal.
try yoga, meditation or prayer
Break your routine, i have to force myself to go to my MOPS group once a month, and actually i think I hate it, but i feel so much better when I come back home.
get as much sunshine as possible, whenever possible.
kick the caffeine
always, nomatter how bad you feel and how little you want to do, shower and get dressed for the day
keep a journal, or two, one to complain and vent and one where you can list all the things you are grateful for. reread the latter and burn the first when it is full.
talking helps, talk here, or to a friend, therapist, pastor, doctor, your husband, anyone who will listen and not judge
and remember, depression is normal and it can be genetic, it's not your fault and it doesn't make you crazy or a bad person/wife/mother