Doctor, I'm thinner so I want to be fat, so which foods have more protein?

Balanced diet. It's not unusual for teenage boys to be thin, and wish they were more muscular. Eat a balanced diet with meat, chicken, vegetables, fruit, whole-grain bread. See if you can start an exercise program that will help you build muscle. You probably don't want to be fat; just gain muscle mass. If you're in school, your coach or gym teacher may be able to advise you.