Height and Weight not right?

ok well i am 15, a boy, and im 5'9 aand my weight varies between 110 and 117 (on a daily basis). so my question is, is there anyway to get 'heftier" i guess you would say, i mean like cuz i eat alot and yet i seem to either lose weight or stay the same, and everyone in family is over 6'0 (mom:6'0, dad: 6'1, brother:6'5, sister: 6'2) so i dont know if its because my metabolism is soo high or idk, but im underweight for my age im guessing, and i believe im a late-bloomer, i eat decently, not many fruits tho, so idk whats the deal