I suffer the same hives. I have since I was diagnosed with cancer.
At first it was the excessive billirueben, in my bloodstream. After the whipple, they would come on at such random times, that I too was ask if I changed laundry detergent, shampoo, ect ect.
We are now five years later, almost.
I do know that I can not eat anything with red flavoring or coloring.
Also, I stopped taking all my meds, then added them back in one at a time.
It was none of those.
Anyways, after five years, I have diagnosed myself. Bread and butter.
I don't know yet if I have developed a wheat allergy, ceilic, or gluton, or even just the yeast in the bread. I just know that I stopped eating bread, and the hives are gone.
The reason I don't think its a wheat allergy, I can eat waffles, pizza crust, pie crust, and no breakout. Not to mention, both my Grandparents were wheat farmers and I have been around it my entire life.
I have my next Dr. apt the first part of next week and will see what he suggests in the form of testing.
I hope this gives you hope and an idea or two on how to figure out what is causing yours. I wish you the best.