Hi, welcome to Healingwell! :) This rash could be from anything so it's good that you are going to see an allergist. But in the meantime, you can check out this website: http://www.dermnetnz.org/
I visit that one frequently because I get frequent rashes myself with no rhyme nor reason except mine don't itch but they burn. I'm still trying to figure it out. I haven't seen an allergist yet either but I don't think mine is allergy related. If you go see the allergist and they come up empty handed. Take a picture of these rashes and see a dermatologist. Maybe they can have more insight to what is causing this. If you find out anything, come back and tell us if you can. I'm curious as to what it could be myself.