Came here to say a similar thing: I was suffering for years with palm-sized hives all over my torso. My wrists and ankles were covered in scratched-open sores. the itch drove me to near insanity. I thought is was external/environmental as you are postulating - because it is on the skin, so I tried cutting all soaps, shampoos and washing detergents. To no avail.

It was a gluten allergy. I was told by a naturopath that wheat was no good, but a couple of decades later, the reactions had bloomed to include a sensitivity to all grains, except for white rice. Furthermore, my sensitivity had expanded into anything with round-up - so root vegetables (which are harvested by 'killing the green stuff' with round-up before the harvest. Problem is, as the plant dies, it desperately directs everything, including the round-up, to the root).

To cut a decades-long story short, this is what cured me: Try eating a Carnivore diet for about six weeks, and then re-introduce other foods One-at-a-time. What have you got to lose? It does not have to cost more, surprisingly.

This means aim for about a pound of meat, with plenty of animal fat, a day. Nothing else except water, black coffee or tea. One of the first things you can experiment with is other animal products, but some people react to stuff like seafood, eggs, or dairy - so that remains for you to find out. The 'safest meats are beef, deer or goat. I find lamb, chicken and pork very acceptable myself, but you need to figure that out for yourself.