My hips are so boney and I just want to gain weight

The weight never stays on though because I never have an appetite. I gained .5lbs and I thought I was doing well but noooope I apparently lost weight bc the next week I stepped on the scale it said 116.7

I want to be 130ish but that seems like it's never going to happen. I don't understand if I don't have a thyroid issue than why the heck cant I put on any weight. It's so discouraging.

Im 21 years old and my face and body look exactly the same way as when I was 15