Hi ! It looks like some kind of allegic reaction to a foreign substance. Have you changed the brand or fabric of the underwear you wear following which the problem started ? If there is no such history, please get your blood sugar tested. Sometimes we miss this basic test which might be the cause for your skin problem. In the mean while please do not scratch the skin of your scrotum
as it may lead to severe infection both in diabetics and less frequently in non diabetics. Also you can try olive oil application after your bath and getting yourself dried up. It helps in many irritable skin problems. Wish you an early recovery.