>>>Case in point. because some decongestants could be used (in large enough amounts) to produce meth, I now have to go to the pharmacy and have my driver's license recorded because I live in the middle of the allergy capitol of the world and I like to breathe on occasion. And because there are two of us (my husband and I) who are silly enough to enjoy that whole breathing thing, we can go through a 10-count box of decongestants fairly quickly (husband takes normal dose, I take 1/2 dose). And while I can get 2 10-counts, I can't purchase 2 20-count boxes BECAUSE I MIGHT BE MAKING METH. Or so the logic goes. Nor can I purchase 2 10-count boxes more than every two weeks.
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>>Side note - have you or your husband ever tried cutting out caffeine to help with your allergies? I used to be the same as you - miserable this time of the year. I haven't had to touch decongestants or antihistamines for about 10 years now.
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>>If you try it you likely won't see immediate results. Caffeine is fat-soluble and stored in body tissues so it takes a while for it and its byproducts to disappear. In my case it took about a month.
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>>Besides the usual suspects of coffee and tea, there's lots of caffeine in almost all soft drinks and energy drinks.
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>I wonder if there is an aging component to it. I used to get bad hay fever every spring. Around the age of 40 it disappeared, even though I didn't change my intake of caffeine or make any other behavioral changes that I can think of. Weird. Not that I'm complaining. It was not a severe problem, more of a nuisance; runny nose and sneezing the first hour or two of every day until the antihistamine kicked in.

Could be. In my case it was caffeine, but that's a sample size of 1.

I think if you ask any GP they would say the word "idiopathic" was invented for use in diagnosing allergies :)