Thanks all for your responses.
Radd, you sound a bit like me with the allergies which have been lifelong for me. The hissy ears with drinking struck a cord with me, and I even go a bit deaf, as well as very flushed, especially with wine and champagne, a classic histamine response. And post nasal drip has been my life for 40 years! Along with a multitude of other allergies since childhood.
I've suspected recently that I have histamine intolerance (after discovering it quite accidentally) and think it's having an impact on my thyroid, and vice versa, a kind of vicious cycle really. I've ordered the DAO replacement enzyme and I'm waiting for it to arrive, so I'll see how I get on with that, and I've switched my probiotics to the type that helps clear histamine. I have a multitude of digestive issues including coeliac disease, so it wouldn't surprise me at all to have a low or missing enzyme. I'm also going to try vitamin C in therapeutic dosages. I'll try all these treatments one at a time so that I know whether I have a good or bad reaction, or none at all.
All this is what has lead me to ask about Quercetin on this forum, it's something I can also try instead of OTC antihistamines and I've read that it can regulate mast cells as well, which also helps with histamine intolerance. However I'm cautious due to its potential impact on my thyroid. I've had quite enough of my thyroid not behaving over the last couple of years so I shall wait and see with that one.
As you can see I've done my research and have got the book suggested on the way too (I'd already earmarked it online).
I've been on a real journey with my health for some time now and have seen no end in sight, and the NHS just want to prescribe a pill for every ill or refuse to recognise obvious issues and gaps in health care. The whole histamine intolerance thing just seems to really make sense to me and I wouldn't be surprised if I've always had it. I'll just have to wait and see what happens with my experiments.
My doctor is actually very good and I always tell her what I'm doing and she monitors me alongside her conventional treatment, she's just bound by the narrow and sometimes archaic rules of the NHS.
I'll report back with the results of each thing I try, at least maybe that way it can help others who don't know which way to turn next, people who just want to feel well, and normal, again.