I don't remember where I read or who I was told by so Idk if it's true or not but it seems worth a shot. If you don't know if you're allergic to a certain plant or not, you can take a leaf from it (think it might have to have juice still in it so you might need to find a live plant rather than using a bud that's been cured) and rub a little on your wrist and wait (don't remember how long sorry, think it's like 15mins) if the spot looks and feels normal after the time has passed you aren't as likely to be allergic, but if the area turns red, swells, begins severely itching or burning, blisters, breaks out in hives or looks/feels abnormal you're allergic (I imagine it would be difficult not to let yourself start to believe something is wrong when it's not, I'm high and forget the word for it psychosomatic or something). If you don't pass that test then you are very allergic and should avoid it.
Another problem could be the weed is contaminated by something. Are you storing it all in the same container or bag? If so there's a possibility it's coming into contact with some type of contaminant like fungus left in the container. Is it all coming from the same grower? If so it's possible they're using a pesticide or something that you're allergic to. I'm trying to think of anything else that could be causing it because not being able to enjoy weed would be horrible.
I would've thought the antihistamines would do the trick but it seems like they don't. What antihistamine did you try? I would personally recommend good old diphenhydramine (Benadryl) 50mg should be a good dose (if it's the one you already tried then I'd say hydroxyzine at the same dose if you can get it), Benadryl is usually the antihistamine of choice for ER doctors (I'm allergic to a lot of medications mostly just antidepressants and antipsychotics, thankfully not the good stuff , anyway back to the point, every time I had one serious enough that I had to go to the ER the first thing they did was start an IV and shoot me full of Benadryl I'm still alive so I guess it worked haha). If you decide to retry the antihistamines (which I'm honestly afraid to recommend you to consume anymore weed because you said the reaction caused difficulty breathing) you have to make sure you give them enough time to kick in before you smoke/vape/eat 30-45mins should be enough.
Just be cautious, if something is causing difficulty breathing it's something to take seriously. If you try it again I'd recommend having a friend with you as well as a few "fast acting" Benadryl gel caps even if they don't make all the side effects go away they could be enough to stop your airway from swelling completely shut and an aelbutreral inhaler is also a great thing to have for any type of difficulty breathing I'm sure someone you know has some just lying around that they'd give you (I never try a new drug without aelbutreral and Benadryl close by just in case.) Good luck I really hope it isn't the weed and/or you can find some way to enjoy it.
