I don't know how old are you, and how ofter you masturbate or your masturbation habbits, but this is normal when you masturbate often and without any lubrication. Or if you use some toys. I advise you to slow down in your masturbation and to start wearing boxers. the brief, speedo style are not good for the male anatomy and they hurt you penis sometimes, some people believe children should use only boxer because help the normal development of the penis, and briefs slows down the growing of the member. I hope I was able to help you. Also and by the way when you have often sex you may get a rash in the gland of you penis which is normal and is not a rash at all, some people callled "rubor" also some clothing soap may give some rashes.