How do I gain weight?

I’m 17 and 5’5 and weigh 102lbs. I used to weigh 120 in July but got really sick and haven’t had a big appetite since. I’ve been to 2 doctors and they put me on meds that make me feel even worse. I stopped taking them a couple days ago.

Ive been really weak/ frail and when I was play fighting my boyfriend I literally fell over and he didn’t even push me hard. I laughed it off

I’m so insecure now because I can’t even wear low neck shirts because of my ribs on my chest. I don’t want to look like I’m starving myself because I really don’t have an eating disorder.

Any tips on how to gain weight?

(I’ve tried eating a lot of junk food it doesn’t work)