Basically, I masterbate once, maybe twice a day. Recently, I have noticed what looks like swelling or inflamation on the left side of my penis, under the skin, where the shaft meets the head. It is not a blister by means of exterior skin abrasions, it looks like it is happening under the skin. Is this caused by excessive masterbation, rubbing to hard or the wrong way? It seems that if I stop for a couple days the swelling goes down, but the next time I do it, it swells up again. Should I just lay low on the masterbation for a while and let it heal or is there a serious problem. I should add that i've been with the same partner for a year and a half now, been tested for stds and was normal and so was she.