See a doctor. Not likely to be related to a superficial fungal infection. This needs to be seen and a history and exam obtained to establish the cause. Good luck.
Fungal infection right armpit, Rx ketoconazole 2x day, small scar from mole removal 2 months ago has turned red and raw rest of skin ok, what to do?
Treatment review. In general such problems require keep area clean and dry, gp should take samples to confirm its a fungal infection (which is less common than bacterial). Treatment needs to be changed accordingly.
Intertrigo. "Fungal" unlikely. No harm from ketoconazole, might help. Ventilation and cool water rinses are useful. If it persists see a dermatologist. Meanwhile you can try OTC hydrocortisone.