It's possible to "loose" jaw if you loose weight?

[Cartman1]

I look like this, but before with more weight my jaw was good, not so thin, idk of it's that or what, but I lost weight because I can't move for the pain of a problem with a surgery, so I lost a lot of weight.

 

[Cartman1]

It's there a way to gain weight? I just gain 6.6 pounds per year since I was like 14 or something like that, I'm 19 now and like 5"11 or 6"0 so the weight it's too low and you can see it, but idk how to gain weight, it's incredibly difficult, I eat a lot and don't gain weight