itchy bumps on body

Trying to figure out what is causing all my itching. It started 2 months ago. Throughout the day I break out with small pin-head size bumps that itch like crazy. I went to an allergist who diagnosed contact dermatitis and put me on prednisone. I've been on it twice and it works, but once I stop treatment it comes back. I haven't changed any lotions, detergents, etc - and we use all perfume-free stuff. I switched brands just in case, and still not better. It's not scabies because it's not on my hands, fingers, creases, etc. No signs of bedbugs anywhere - husband not getting bit - and prednisone would not help that. Gets worse after exercise or drinking alcohol - both histamine producers. Can't think what I could be eating that's causing it. If it was contact derm from detergent or something, wouldn't it be on my face, too. Mostly on stomach and back - some on arms, legs, chest, buttocks.