We had a very hard time figuring it out, and I’m not sure we ever figured out some of his outbreaks.
Medications and foods are typically easier to identify (my son had penicillin allergies), as you can look at what the recently infested. Unfortunately for us, my son also had some environmental allergies that were harder to pinpoint. Ultimately, it seemed that he was sensitive to some detergents and cleaners and some animals. But it was super frustrating and there were days where he was itchy and miserable with hives just like those and I don’t think we ever figured out why.
So, if you recently changed laundry detergent, or had your carpets cleaned or car detailed, it could be that. Hopefully this is a fluke thing, but if not he’ll probably grow out of it (my son did after a few years).
Hoping for the best for you and your family in this, I know it’s not fun.