How are you extremely skinny? Do you have a digestive issue or something?
I struggled with weight gain for many years due to crippling IBS but I found some relief while bulking from a certain probiotic. (Got lucky - dozens of things I tried including fodmap, etc. never worked. That said, the probiotic only helps - not solves... and doesn't solve my absorption issues)
Surgery, steroids, and a serious bulk are in order if you're serious.
I struggled with weight gain for many years due to crippling IBS but I found some relief while bulking from a certain probiotic. (Got lucky - dozens of things I tried including fodmap, etc. never worked. That said, the probiotic only helps - not solves... and doesn't solve my absorption issues)
Surgery, steroids, and a serious bulk are in order if you're serious.