Suggest Cure For Discolored Spot On The Penis

I've been with the same woman for over a year now and 2 days ago I noticed what looks to be either chafing or a small discolored tiny mark on the left side of the head on my penis. I hadn't worn boxers for the past 4 days so Im wondering could it be chafing since not only did I not wear underwear but I masturbate a lot? I havent cheated and neither has she so I can't see it being an std