What Causes Lumps On The Penis?

ok so i was masturbating about an hour ago and as i was, i noticed a growing pain under the tip of my penis. eventually, i stopped and turned on the light, and there was a red bump where the pain was. i ve never seen anything like this before. is this just soreness from masturbation, or could it be something else? I have never had intercourse, but i did give a girl oral about a week ago.