Suggest Remedy For Red, Blotchy Rash On Both Upper Arms And Around Armpits

For four months I have had a red, blotchy rash on both upper arms and around my armpits. It does not itch it BURNS like crazy. It started out on the outside of my right armpit as a small bright red mark that burned and then within 1 week or two both upper arms are red, blotchy and burning. I have tried several corticosteriods creams from my dermatologist and nothing helps, it seems to be getting worse. My dermatologist has no idea what is it. It is not a raised rash it is just red and blotchy and now my skin is thinning and I can see my veins more clearly. Help!