What to do about painful skin rash like blisters on red areas?

Depends... ...On the distribution. If you have painful blisters in a single band on one side of the body, that's shingles. If the blisters are widespread, it could be viral (herpes), bacterial (impetigo and others), or a contact dermatitis (poison ivy and many others) that may be getting infected secondarily. You should see your doctor or a dermatologist for a precise diagnosis.