not to nay say anyone, but I have a strong reaction to high pg products. When I went to the all vg (remember now flavorings have pg in them, you just can't totally get away from it. ) I had less difficulty. Also I have better luck with the pain in the .... ceramic cartos than I do with cartridges and the cartos with fluff in them. Every vaper is different. Every vaper's lungs recover at a different rate. Your lungs could be trying to get rid of the damage years of smoking has done to you too. You may also have a cold.
I'm not saying any of these things are true specifically to you, but these are things you might consider, maybe vg irritates you, maybe pg does, maybe it's the cartridges/cartos you are using, I doubt it's the level of nicotine that is causing the cough (from my experience it seems too high nicotine tends to make you nauseous rather than have coughing issues.)maye your lungs are refreshing themselves , maybe you just have a cold. What I'm saying here is, don't give up. Consider all the things people have mentioned here , and one by one, rule each thing out till you find out what it is that is making you cough. Don't throw the baby out with the bath water.