I eat like mad but im very skinny in 13 but small an I eat a lot of food an still be hungry?

Malabsorption. Many people would envy you, but you need to rule out malabsorption (can't absorb food) / maldigestion (can't break it down). Your physician may do a fecal fat or d-xylose test or screen you for common causes of malabsorption such as celiac sprue. This is infamously easy for physicians to miss. I'm glad you're taking a pro-active approach to your health. Good luck.