After 40 years I smoking, I was having major sinus issues. I woke up every morning to major congestion which always took an hour or so to clear. When I switched to vaping, I noticed the morning congestion starting to subside, but in it's place I had post nasal drip which caused symptoms like you describe. What I think happened is without all the chemicals in cigarettes, my body was better equipped to deal with the congestion, allowing my sinuses to drain. Eventually, the post nasal drip subsided as well. I still have seasonal allergies which require the use of loratadine, but I no longer have to medicate myself year round.
The advice about drinking plenty of water is also important to keep in mind. Not only for the reasons stated above, but because vaping can cause you to become dehydrated which can lead to muscle cramps if you don't increase your water intake.