I have multiple allergies, and hives is one of my frequent symptoms. I don't handle standard medicines well, so I've done some experimenting. The BEST thing I've ever found for hives, as well as for itchy eyes, sneezing, etc., is a homeopathic remedy. There are several that are good for allergic symptoms. I get best results for MY symptoms from one called histaminum hydrochloride, which I use in the 30C strength. Symptoms start going away within 10 minutes, and within an hour I've had some hives completely disappear. Because yours have gotten established longer, your results could be slower, but you should be able to notice an improvement pretty quickly if this approach will work for you.
Since medical science has no answers, you might want to contact a homeopath. The initial consultation is lengthy and will probably cost you a couple of hundred bucks, and you could be in the 20% of the population who does not respond to this approach, but if you're desperate for relief, you may be in the 80% who find this approach nearly miraculous.
Or you could do a little research of your own, and try the few remedies for allergic reactions that are available in health food stores over the counter. They often have books available right there at the display that can help you decide which remedy to try first (based on your specific symptoms). Each tube of pellets is about $7 - $8, so you can try two or three pretty economically. If they work, you'll know within the first few doses. If they don't, try the next one on the list.
Or you can google "homeopathy for (symptom)" and find the information.
There is almost no incidence of side effects (for some remedies, you might notice a mood change, at most – these are referred to as "mentals"). You don't need to use more than one or two pellets at a time, though the instructions usually suggest three or four (I think this is because people don't believe one or two could possibly work). For me, one dose does the trick, but you may need to use this a few times a day to keep symptoms under control. Don't take more than actually seems to help.
Good luck. I don't know what I'd do if it wasn't for my little tube of homeopathy.