Today I went back to the allergist. I saw a different PA than I'd seen before. We discussed my blood test results.
Great news--there is nothing in my bloodwork indicating an autoimmune disorder or any other disorder! The one thing that was really high was my IgE level. You can read more about IgE here. High IgE indicates an allergic response to something. And mine was really high (normal is 290 or less; mine was 1399. The test was done 8 days after my hives started, when the hives had mostly gone away.)
A week ago, I had almost weaned off my antihistamines, when I again got hives. They were mild, but I had to go back on my meds. I am again in the process of weaning off those medications so that I can get my skin testing done for both food and environmental allergies. If the hives return, we have a couple of other medication options we can try that won't interfere with skin testing.
I did find one thing in common that I consumed before I first got hives, and before they returned last week. Both times, I'd had licorice root. Weird, huh? The first time, I'd had an herbal tea (Tazo Cocoa Mint Mate) with licorice root in it; the second time I'd had some fancy root beer with licorice extract in it. The allergist told me they can do a skin test for licorice extract if I bring it in with me. (Unsurprisingly, it's not on their "top 100" list of foods they are prepared to test for!) I just ordered some on Amazon, and I'm definitely curious to see if I react to it.