Bad eating habits

I have been eating really bad lately, and I haven't been eating the best of foods. I am breastfeeding, so I try to eat as good as I can. My main problem is I'm not eating enough food. I find myself not hungry and I am lacking on drinking water. I used to drink over a gallon a day and now I can hardly drink half a gallon. I have postpartum depression so I know that's probably the main reason for my eating habits. I'm going to see my doctor next week. Hopefully I can get some help.. I just hope my milk supply wont go down because I'm not eating as much as I should be.