Walnuts and almonds do that to me now. Before primal they were fine for me to eat.
Occasionally now I'll have a meal from somewhere I don't usually eat and I get that intense pain. They must have used an ingredient that is high in histamine which causes the allergic reaction. Without grains to offset the histamine (grains have anti hostamine in them) the pain is intense. You just need to find the ingredients that trigger you and avoid them.