Itchy Abdomen, Backside, Red Blotchy Marks All Over, Rashes. Cure?

A couple of nights ago I woke up in the middle of the night with severe itching to my abdomen and to my backside. When I went into the bathroom to inspect I was shocked to see I had developed large red blotchy marks all over my body. The itching is intense and comes and goes. I took a Benadryl to alleviate the problem but it is only temporary. Today is day 2 and it seems like it has gotten worse. My elbows, feet , neck, abdomen, backside, and even one of my palms has a rash on it. The rash is not raised, it is completely flat.It is only welt-like if I have been aggressively scratching it. The rash is also hot to the touch. Leading up to this hive-like rash I have not eaten anything different or anything that I haven t eaten before. No new detergents, soaps, or lotions either. Help please, this is baffling!