Hi, I don't know weather your GP has performed any test or it was his clinical judgement, I think there is no harm in trying an anti-fungal cream, as this is a common cause of problems, like your's. It may also represent an allergic reaction
to a new product you have tried or new garment material you are using, analyze yourself & if the answer is yes stop it at once. Some times overuse of perfumed or antiseptic soaps also cause such problems, if that is the case stop it at once. Third & most important is get your blood sugar tested ( fasting & two hours after meal), as a new onset diabetes
may present this way! If all this fails then you should go straight to a dermatologist
. A skin specialist is the most appropriate person for you to go....best of luck.