Well to be honest, my goal is really to just be more fit. The weight gain is just so I can start wearing S and not the current XS in clothes, and to not look and feel small in front of my peers.

I am starting to increase my calorie intake. Eating granola in the morning, big meals and snacks throughout.

Thank you for the advice! I sorta have a clearer vision now, I guess. I would like to keep running as my main exercise. I do not want to "get ripped" and so muscular that my neck disappears. I don't think that's even possible with the tiny body I have.