I Have A Skin Allergice Reaction, Can't Seem To Track

I have a skin allergice reaction, Can't seem to track it to anything new like clothes, soaps, insect bite, etc. I have been to the Derm and rec'd steriod cream 5 dayas ago. Three days age I started predizone 5 mg. I have no change and ich like crazy, I have a few welts but interestiangly they are bilateral. INside knees, on each hip, elbows, now comiong to my back. It might be from a new cholestrol medicine. I took the medication a few montahs ago with no reaction but maybe this time my body is reacting??? Any thoughts?