I have a rash on my side that looks red and blistered. It is painful and itchy. What could it be?

Shingles, contact. Could be shingles, if it's concentrated in one narrow band and stops at the midline. If not, it could be a contact dermatitis, such as poison ivy, that has become secondarily infected. Either way, pain is your body's way of telling you to get some outside help. See your doctor.
Shingles. Have your doctor check this; it can be treated and sometimes there may be complications.