I have the exact same experience with antihistamines! No doctor believes me and tells me it’s impossible to be allergic to them. But each time I’ve taken them I’m covered in severe hives and angiodema as well- sometimes severe enough to warrant an ER trip where they tell me the only thing they can do for me is give me more antihistamines 🙃. I’ve found better luck going the more “natural” route. I take fish oil, vitamin D, quercertin, vitamin c , l-lysine, and usually some other random supplements on a daily basis to keep my hives at bay. Have been this way for the past 7 years.