Itchy Rash On Elbows, Knees, Calf After Eating Pickle. Taking Medication, No Improvement. Remedy?

I have a very itchy rash that started on my elbows then knees calfs of both legs lower back and butt cheeks after eating homemade pickles made with old white vinegar that had slim growing in it, I boiled it first before adding it to my pickles but I been full of this rash ever since, I went to my doctor and he gave me a shot of prednisone and I am using cortisone cream, it's over a week now and I still am itching and full of this rash, any suggestions.