Suggest Remedy For Red Swollen Penis

Hi,My 5 year old just told me that his penis hurts. When I looked I noticed it is red and a little swollen. He says it only hurts when he touches it and a little when he pees. He does nor remember if he ijured it today, but he had some tight pants on. Is it possible that this is from rubbing against those pants or could it be something more serious? He is uncircumsised and we never had any problems with it; we clean it well daily and it doe not look infected, just a little sowllen and red.