I can’t pull down my foreskin completely when erect?

I am 17 and when I am erect my foreskin doesn’t go down on its own and when I try I can only get it down about 15 percent . When it’s not erect i can pull down my foreskin no issue. But when I try and pull It all the way down it hurts. What should I do? (When erect there still some foreskin covering it unless I am really erect then I can barely see the top part)