I Have A Rash On My Right Hip And Back

I have a rash on my right hip and back that is tender to the touch. Does not itch and is only slightly warm to the touch. This started four days ago and seems to stay the same. The only medicine I take is Benazepril, 10mg daily. I have taken this med for approx. 40 years with no problems. I'm trying to determine the cause, insect, allergy or whatever.