Hello,
There are a few possibilities for this kind of rash.It can be a fungal infection(Tinea cruris) or a contact or irritant ( xerotic) dermatitis.
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 underwears and change them twice a day. and do not share other people’s towels.Application of local antifungal cream(terbinafine, clotrimazole, econazole, ketoconazole, miconazole) and oral antifungal drugs are the mainstay of treatment.If it is contact dermatitis,then oral antihistaminics and steroids are useful.
Treatment for both is entirely different.I feel that you should consult a dermatologist and get it assessed so that specific treatment(antifungals or corticosteroids) can be started.
Hope it helps.Take care and pls do keep me posted if you have any additional queries.Kind regards.