Why when I pull back my foreskin and touch the penis it hurts?

Balanitis, phimosis. Tight foreskin means that smegma can collect under the skin and irritate the glans . Inner surface of foreskin and glans can also get inflammed. A tight frenulum, between foreskin and glans can also be painful. Your foreskin should retract easily, otherwise suggest you consult a urologist. You might benefit from 0.1% Betamethasone cream applications or a circumcision or prepucioplasty.