Suggest Possible Treatment For Rashes On Skin On The Buttocks

I have a rash on my butt, that itches something awfull. I wash my fanny every 3 to 4 hours with cool water. it helps for aqn hour or so. last week I did the 7 day Monostat medication and the 8th day it was still there..I have used Diaper rash cream, and now using aveno moisture cream; also my anal and top crack of butt is also itchy and I have been treating it.. Oh by the way I am 69 and have not been sexually active for 3 yrs . Thank you for any help you can give me...