I agree that lower nicotine, and shallower inhales, makes more sense than cutting down on the part that carries the flavor -- the PG. For a while, a smoker's sense of taste is rather muted, and this persists for varying lengths of time after quitting; going lower on the PG means your juice will have less flavor, and therefore might be far less satisfying. It's true that some people have allergies, but that would manifest in odder ways than in a cough -- rash, anaphylaxis, nosebleed, would be more likely symptoms of a true allergy. But you really shouldn't lung-hit vapor when you're first getting used to it; it's quite different from smoke, and you don't get nicotine very efficiently that way in any case. I never did lung-hits with cigarettes, but I did inhale *directly* and very quickly from my mouth deeply into my lungs; now I "pull" at the vapor in the same way I did cigarettes, like sucking on a straw, but I do it more slowly, and let it hang around in my mouth, throat, and nose for a bit before inhaling; I get less irritation of the lungs that way, and much better absorption of nicotine.
And while it seems to be somewhat rarer than PG sensitivity, there are those of us who are far more sensitive to too much VG, than PG; it's very thick, very viscous, and for some people that can mean anything from a heavy, tight feeling, all the way to being completely unable to breathe. Some VG is necessary, as it makes a lot better vapor than PG does, but I find that keeping it (VG) at 25% or less gives my lungs farrrrrrrrr fewer problems.
Andria