I was vaping 14hrs plus a day for several months...and finally found some juices I really loved....just odd that this came about out of the blue. I would have figured if I had a problem with PG that it would have shown up earlier.
It would not surprise me too much that irritation leading to what you are experiencing could develop over some time. Allergies certainly are like that. And symptoms don`t always match exactly.
If you do try glycerin and it`s too thick to wick properly, add a couple of drops of water at a time until it is thin enough. It will not take much. Tap water will do it for a tankful. I would use distilled water for longer term thinning.