You may be suffering from tinea cruris which is a very common fungal infection especially in summers.  First of all dont apply any otc drugs like panderm fourderm quadriderm betnovate etc which you get from chemist or any medicine suggested by friend or family without doctor prescription it may harm you and further worsen your disease.  The treatment is very simple just go to any dermatologist and they will prescribe you some antifungals for next 3-4 weeks.