hey, im 17 and recently i've been trying to pull my foreskin back all the way but it wont go. when not erect i can take all the way back but the head is really sensitive. when erect i can take it half the length of the head, sometimes when i get an erection after i've pulled back the foreskin it hurts like hell, its like my skin is stretching and is about to rip.... i get the rolling of the foreskin when i pull it back over the head... i have no trouble masturbating or urinating... please advise....