I'm 5' 9" recently went through postpartum depress & I got down to 80 lbs. My body ate my muscle mass because I forgot to eat. I need it back. Help!

FOOD IS FUEL. It is of utmost importance to get proper nutrition, not only for you but for the sake of your newborn. If you are forgetting meals, i suggest you set your phone/alarm to alert you that it's time to eat. Every 3-4 hours is best for you to keep your blood sugars balanced and your metabolism working.F.
U may have anorexia. Loss of weight can be part of a depression. However, your weight seems to be dangerously low for your height. U need to have a physical exam to ensure you are in good health and then perhaps work with a nuitritionist. Your health is very important for you and your baby, so take good care of yourself.