What Causes Rashes On Back,legs And Buttocks?

I have been using Herbalife products about 3-4 weeks. I started with a serious rash on my back, legs, butt. I went to an allergist on Monday and found out I am allergic to pecans, pine nuts, pistachio's and castein. I am trying to figure out which products contain any of these where the obvious is not listed. Can you help? There isn't anything on there web site. I am 52 - 5' 5" 170#'s