Swelling of foreskin. I am very worried.

A month ago i was masturbating and my foreskin got swollen. My doctor gave me some pills and injection said it was infection. And swelling went away. I avoived masturbation for a month after all this happened. But after a month when i masturbated same thing happened again. Doctor gave me same medications again. Swelling is gone again now. But i see some veins on my penis. They are on sides on top and bottom also. They dont hurt. Some of these veins were already there before. But some veins appeared after swelling incident. I do not know why my foreskin swells evertime i masturbate. It has never happened to me before. I am scarred to masturbate cause i think it will swell again. Please help me, why is this happening and is there something serious about this problem. What should i do. I am very worried.