Can't pull my foreskin back. what could be wrong?

Several things: Problems like these can only be correctly handled by your doctor in person. He/she needs to listen to you, perform an examination and possibly run labs or other tests. That's the only way he/she can find out what's going on and what to do about it.

Phimosis, tight skin: This must interfere with penile hygeine and is unsatisfactory for either sex or masturbation. Definitive treatment is circumcision, although some penises respond to ma prolonged course of prescription steroid cream, e.G kenalog (triamcinolone) or 0.1% betamethasone. Suggest you see a urologist who will take care of the problem.