I believe I figured out the source of my rash.  I am 29 and have never had an allergy in my life and about 3 months ago I noticed an itchy rash all over my lower back, fore arms and abdomen.  It went away but started coming back at least twice a week and recently has been mostly all over my chest.  after changing soaps and lots of research it appeared I was getting hives because the rash only lasts a few hours.  I soon figured out I was getting the rash after eating certain foods on the list of foods that release histamine.  Unfortunately they are my favorite foods:  Shellfish, tomatoes (including tomato sauce), cheese and eggs.  so after avoiding all of these I have had no issues.  This is really going to be hard since pizza and crab have been my favorite foods forever!  I guess I'll just have to carry lots of Benedryl if I have to have them!