Hello,
It can be due to irritation caused by the underwear if you are using brief and sweating and humidity may increase the discomfort. The other possibility is of dermatitis skin or fungal infection. Wash your groin daily and then dry thoroughly by pat drying, not rubbing. A hairdryer is useful if you have hairy groins. The damp groin is an ideal site for fungi to multiply. Also wear cotton underwear and change them twice a day and do not share other people’s towels.
Also apply some antifungal powder on the area and take some antihistaminic like Benadryl for the itching. If the symptoms persist then topical and oral antifungals may be needed.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
It could be any infection or herpes ? did u test for herpes ? do u have any other symp. ?