Black spots appeared on my cock I think last friday and I don't know what it is. I think I got it after I masturbate with my undies on (my brief was kinda rough, but it's cotton). I noticed it while I'm taking a bath and started to worry a bit. I know it's not STD. These black spots hurt a little bit whether I touch it or not. I did put rubbing alcohol on it and it hurts so bad. What could it be? Please help. Do you think those were just wounds from masturbating? ETA: It is itchy too.