What Is The Cause And Treatment For Itchy Rash On Buttocks?

My husband has had an itchy rash on his buttocks and upper thigh area. He's a driver and has noticed since the weather has gotten hotter it gets worse. He's been to see his Dr and been prescribed a couple different types of cream over the past month but nothing has helped. His Dr. says it's a fungus. He likes to drink beer could this be the reason the rash is not going away?