What Causes An Itchy Rash On The Face?

I have had a acne/hives like rash on a localized area of my face for about 3 weeks. It itches at times and flares up without cause. I have been careful about face creams, etc. A topical antibiotic cream that I have been using for almost 6 days has not cleared it up. Have never had a problem before, not even acne as a teenager. I'm a 37 year old female, 5'5", 135 pds. Primary care physician was uncertain about diagnosis.