Hi 'fluffy
Lot's of good suggestions. Fortunately with vaping, if it is something related to vaping, you have flexible options to tweak things.
First, as pointed out you don't need to lung inhale if that is what you are doing. You get the majority of your nic absorption from the mucus linings in your oral cavity anyway. So you may want to change your vaping technique and avoid lung inhaling.
It could be an adverse or allergic reaction to something in your liquid. Do you know the PG/VG ratio of what you are using? In the most general sense PG can be harsh for some people so the solution could be as simple as lowering the amount of PG in your liquids.
You could simply be in an insult to injury phase, with your lungs still clearing out from smoking and right now they just aren't happy with something new being added on top of that. Again, a possible solution is to avoid the lung inhaling for now.
Do you have seasonal pollen allergies? I do and the last two years have been brutal. I don't have diagnosed asthma, but this is the first time in 10 years I have had to resort to occasional rounds of Asmanex (steroid) therapy to deal with upper respiratory inflammation because my pollen allergies have been so brutal.