tips/advice please!!

Can anyone recommend any vitamins/supplements to help me gain weight/muscle? I have lost so much weight since having my second baby 3 months ago and I honestly hate it🥺

I was 100lbs when I got pregnant with my oldest & was about 140 when I gave birth.

with my second I was around 100lbs pre-pregnancy & 115 when I gave birth. I’m 3m pp and back down to about 97lbs. I’ve always been a tiny person with a very fast metabolism, I work out at home when I can (I’m a sahm) and I’m already drinking protein shakes but I’m not seeing any change and I’m just really self conscious about my weight. I would like to be around 120-130 healthily.

Any tips/advice on ways to gain weight is deeply appreciated!! TIA