9 months postpartum HELP

I am nine months postpartum and I'm skinnier than ever!! I was 124 pounds before pregnancy, 156 pounds when I was 9 months pregnant, now I'm 104?? I can't gain weight for the life of me. I have no boobs anymore, no fat on any part of my body. I was a D cup before pregnancy and now I'm a B. Everyday I feel like I get skinnier. I worked out, eaten full meals plus snacks, nothing is working