I'm kinda concerned so... as we all know I had my daughter 3 weeks ago and I'm slowly getting rid of…

I'm kinda concerned so... as we all know I had my daughter 3 weeks ago and I'm slowly getting rid of the pug BUT I'm losing weight, I can't remember when I was able to fit into a small and now I have to shop for smalls left and right... any tips on how to gain weight either supplements BTW I do eat I guess it's not enough and idk what to do