I think I would also keep an eye on the flavor you are vaping when you have problems. A while back my daughter tried a new (to her) flavor from a vendor that we had been using since we started vaping, same pg/vg ratio and same nicotine strength that she had been using all along. She started having a problem only when she was vaping that particular flavor. All other flavors caused no problem. Fast forward to this month, she started having problems with a new flavor from another vendor, whom we have been using for over a year. Again, same pg/vg ratio and nicotine strength that she has been using. No problems when she vapes other flavors, either from that vendor or the others that we have tried. I think there is something in the flavorings used for the two flavors she has problems with that does not agree with her.
Just something to keep in mind when trying to narrow down the cause of the problem.