What Causes Dents On Head?

I'm 19 years old, and only weigh 150 pounds and I have dents all around my head. I just want to know what causes them and is there some way to make them go away, I also have a fatty hump in the back of my head and when I get a haircut it's visible and my cousins call me meat head... I'm concerned because I've only seen this happen to people who are fat and not near fat... it's very embarrassing and I just want to find a solution so i can feel good about myself again!!!!!!!!!!