Since you tested negative for an STD, you probably have either a yeast infection (jock itch), or it could simply be a heat rash.
It could also be an allergy. Have you started using a new soap or lotion?
Keep the area as clean and dry as possible. If you wish, you can try an antifungal cream for jock itch, or some hydrocortisone cream.
I hope this helps,
Kerry
Kerry, RN
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