What Causes Tight Penis Foreskin While Masturbating?

Hi Sir,This is Nagaraj. i am 26. I have not done any sex up to now. but i hava an habit of self satisfaction by doing HP. while doing HP my pennis skin is vey tight. it is not coming back. i am getting pain. when i participate in sex with a women what is my position? and i am going to marry with in a couple of months. please give me a suggestion?