It could be any number of things, from a cyst, to a tumor, to anything in between. The fact that you have noticed a CHANGE is what cocnerns me, more than the fact that you have it. Go to the doctor and have it checked--it isn't worth chancing it for the sake of embarassment. Likely it IS nothing, but check anyway. The doctor won't take any more notice or show any difference than if it was a lump on your hand. You don't want to risk LOSING your penis, do you? Losing it because you were too embarassed to have the doctor touch your penis really WOULD be embarassing, wouldn't it? I know this sounds harsh, but the risks ARE there--don't take unecessary chances with your health.