What Is The Treatment For Itchy Red Rashes In The Hip?

Hi, I am a 23 yr old healthy woman- pretty much stress free. About a week ago I developed a very itchy, red, spotted rash on my left hip. I have been applying cortizone and it relieves it for a while and it starts to itch again but doesnt go away! I have not changed detergent or anything and am not generally allergic to anything. Could there be some underlying cause? What can I do to get rid of it?