How to get rid of an itchy heat rash from over a month ago?

I walk miles per week on a regular basis.....I don't know perhaps 4x per week at 2-3 miles each walk?...ANywho, when it was blazin' hot outside, like 90 and way above w/humidity, suddenly I developed a heat rash that itches sometimes, on each side of the groin, lol. But nope not on private area or private parts whatsoever.

I keep applying 91% rubbing alchohol, then tea tree oil on it + calamine lotion. It stops the itching but the freaking thing will not go away! I wash it with regular soap-n-water then apply all the stuff mentioned above.

ANyone w/this eperience or an actual doctor who can recommend something to heal it safely and completely? THANKS☺