@AnthonyB - I don't get nearly the symptoms you get. However, within a few puffs...I do get an immediate headache at the back base of my head, a tingling sensation in my tongue, and a not quite right feeling...if/when a flavoring I've used for DIY eliquids contains
ethyl alcohol in its base and sometimes if 1 contains quite a bit of ethanol. I've learned to let those eliquids "breathe" for a day or so (with the cap and dropper tip removed) before I vape them. The ethyl alcohol will evaporate off and then it's fine = none of the symptoms at all then.
I know
you don't DIY your eliquids, but the presence of EA or ethanol in some of the flavorings the vendors or manufacturers used to make the eliquids that
you react to...might be something to consider. I especially wonder about the banana and cigar flavored eliquid you mentioned, as banana flavoring is one of them that
sometimes has ethyl alcohol in it. In fact, there are quite a few fruit flavorings and other types that
do contain it. I can usually tell if I take a small sniff of the flavoring, because it'll have a sharp sort of harshness to it that kind of "zings" my nose.
If you've been able to make note of some of the specific eliquids that result in your symptoms appearing right away within a few puffs...maybe you could contact the vendor/manufacturer and simply ask if
either ethyl alcohol and/or ethanol are in any of the flavorings used to make them. They
should be able to tell you that for sure, though it may take them some time to check the ingredients list of each flavoring in those particular eliquids.