I think the same thing, but I definitely don't cough as much as when I was smoking cigs everyday all day.
Also if it hasn't been that long since you quit cigarettes, it may be both the fact you're not used to vaping yet combined with the fact your cilia in your lungs are healing and bringing up mucus is it's way of cleaning the lungs out.. So it could very well go away overtime.
I don't really understand how PG allergy works, how some people with a PG allergy can take just one puff off a 100% PG juice and feel like they are going to die but take 10-20 puffs off a 20/80 PG/VG mix in a short time and feel perfectly fine, that doesn't make much sense to me..
It could be a PG causing you to cough I guess either due to a allergy or since it's harsher on the throat, or it could be the VG, since VG is thicker and stickier that could be acting kinda like a adhesive, making mucus in your throat or lungs form together easier? I think drinking a lot more water might help that, sooth the throat while diluting the mucus and washing it down at the same time.
Of course this is just my opinion, I have no science to back it up. I'd suggest trying both a higher PG and higher VG juice (Or all PG and all VG if you're feeling brave) on separate days and see which one might be causing the problem, or like I said since your lungs are healing it could go away over time.