Why doesn't a Cortisone shot plus Prednisone - Zyrtec and Benadryl not help me with my Sulfa allergy?

I began a medication (400mg a day) on the 28th of Dec.and when I woke up on Jan. 10th I had red spots all over my chest and underarm areas. I checked the drug on-line and learned that it had sulfa in it. When I woke up the next day it was worse so the doc gave me a cortisone shot and told me to take benadryl, to discontinue the medicine and to take Aveeno Oatmeal baths. Two days later it's worse, the spots cover more of my body including face and eyelids. The doc prescribed a regimen of Prednisone and for me to switch from Benadryl to Zyrtec for the itching. NOTHING HELPS. It is now Saturday the 15th and it's even worse. The palms of my hands, ears and scalp are now covered and I also have a sinus infection that the doctor can't treat. I am at wits end and wish I could just come out of my skin. Do you have any suggestions? Could the Prednisone and Zyrtec be doing the opposite to me - making it worse - or does it have to get worse to get better?