Girls, hello!) Could you please tell me, after childbirth I started lo…

Girls, hello!) Could you please tell me, after childbirth I started losing weight drastically, I can't gain any weight back, I don't even know what to do anymore? I lost all the weight I gained during pregnancy and became thinner than before pregnancy. Are there any vitamins that could be taken while breastfeeding? Also, my hair is falling out terribly, like half of it has fallen out from my head, maybe some advice would help too, I will be incredibly grateful.