Environmental, food, even cohabiting animals can cause allergies. And when you include autoimmune responses things get really tricky. I know a dog whose Vet told her she was allergic to cat dander. (Her best friend was a cat.)
Pollen, mold, fertilizer, weed killer, all of these can cause reactions. I agree that it sounds environmental since it started with a geographical change. There could be mold. Or fleas.
Maybe parasites are much worse in the new environment, and it only takes one bite to cause skin flare ups.
Check for trees that were not common in your old neighborhood, watch the pollen count and keep record of changes outside that coincide with your dog’s reactions. (Or lack of.) Feed water packed sardines! They do not live long enough to gather metals or toxins, they are not processed like oils, and are way more fresh than supplements. My dog drinks the sardine water and gobbles up the little sardines. Be sure and get water packed!! The cans are around $1.00 in the grocery store and you know that it is human grade. Win! Win!