Hello,
Such a painful rash can be due to herpes zoster or shingles or cellulitis skin. Cellulitis is an infection of the deep subcutaneous tissue of the skin. It can be caused by normal skin flora or by exogenous bacteria. Get an evaluation done from a dermatologist as you may need oral antibiotics.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I wonder whether you have broken out a herpes zoster rash.The feautures seem to point out to this.