Foreskin won't stay down!

Hi Im 15 years old, i have problems With My foreskin. 

I Can pull My foreskin back when IM soft easy, I Can also pull back My foreskin when erect After a shower With a little force. But Every time i pull back My foreskin under the glans a bunch of skin folds up and it looks Weird, it does hurt a little bit at the string of My penis, but i Can take the pain, but everytime i pull it back it won't stay back, it always goes up again, what should i do, please HELP!! How do I get the foreskin to stay down when erect and how do I remove all the bunched up skin?!!