What Do Red Blisters On The Body Indicate?

I have a red, angry-looking rash with what appear to be blisters or bumps. It has been a recurring problem for several years. The first time it occurred was when I was in mid-thirties. It lasted for over two years, going from one area of my body to another. My PCP tried and sent me to a dermatologist who treated but did not get rid of it with prednisone pill therapy. Next stop was allergist. All tests were negative. I treated at various times with alcohol spray to keep infection at bay, and rubbed with either over counter athletes foot cream or chest rub. One dermatologist, who is retired now, gave me a shot, RX cream and two weeks later followed with second shot. It took care of the problem. Have NEVER gotten a diagnosis.