Sorry about the spelling mistakes, time for bed, I dont have a scrotup but I did have a scrotum last time I looked.
My friend I suffered what you have for over 20 years, its called Jock Rash very much like Tinea that gets between your toes and stinks like hell, mate I used to scratch myself to pieces because it used ton itch so much, mine used to cover the area from behind my my scrotup to my anus and sometimes used to spread into my groin area..
This is how I fixed my problem.
My wife and I got a bit carried away about 20 years ago and decided to shave our genitals, I shaved all the hair from my penis, scrotum, belly and as far back as my anus, low and behold the jock rash vanished and has never returned, I do however still shave all the hair of my genitals, all this long before it became trendy to shave the hair off your genitals, it fixed me up and I am as clean as a whistle down there.
Give it a try,it sure beats that stinking Jock Rash.