it could be any of the things that you mention including a yeast or bacterial infection or even an std – but that's something that only a trip to the doctor can reveal. my guess from the limited information available is that it is likely to be a skin irritation of some sort which can occur for a number of reasons. if it is a skin irritation using a first rate penis health cream (health professionals recommend man1 man oil) should help. look for one that includes a first rate emollient like shea butter as well as a powerful antioxidant like alpha lipoic acid. good luck!
small red bumps on penis forskin after and head also pink irritation on base. happens after masterbating or intercourse. first thought it was contact dermatitis with my gf but it becomes irritated after masterbating too. it's very mild and not that noticeable unless you know it's there. when we were not using protection and had frequent intercourse it would become more severe and would flake the day after. could this be a yeast infection or some kind of bacteria?