I can't retract my foreskin at all. What can I do?

I've been masturbating for a while now, since I was 11. Even when I was younger I could never retract my foreskin, and it hurted to try. Now I'm 13 and I still can't. I can masturbate and ejaculate just fine (it comes out, but I have to keep dabbing at it or pee, or some will "trickle" out), but I'm worried about 2 things. One, will this cause a problem if I have sex, and two I heard that stuff collects under there and can give you an infection. If so, how can I get it to retract?