Rash on groin area help me find out why?

Try antifungal cream. The most common cause of a rash in the groin area is called tinea cruis or "jock-itch". Try an over the counter anti-fungal cream like Clotrimazole or lotrimin (clotrimazole). After one week, if these don't work then you may have seborrheic dermatitis. This requires a prescription from a dermatologist.