I Have Had An Extremely Itchy Red Rash On Neck,

I have had an extremely itchy red rash on neck, chest, arms and torso for 6 weeks. Prednisone and Benadryll help, however it returns as soon as I go off the prednisone. I have eliminated all possible food allergens from my diet, as well as environmental allergens. Topically, Vaseline seems to help the most.