I'm not a doctor, but I can speak from my personal experience. I've experienced the ear popping and occasional canker sores, as well as other strange symptoms. What worked for me was lowering my pg level to 30% and avoiding juices with my known allergens (dairy & coconut). My recommendation, see a doctor and get allergy tested (including food allergies). In the mean time, change your e-juice and drink plenty of water to help flush your system. If you think it's an allergic reaction, take an otc allergy medication (however, you must be off allergy meds for a few days before being allergy tested).
Before you ask, yes you can develop allergies later in life. I only found out about mine 5 years ago. Also, my body can't distinguish between natural and artificial vaping flavors, so any e-fluid with milk, cream, or coconut flavorings, gives me an allergic reaction. I also have to be careful about which vg is used.
I know others have said to see a doctor, I agree, but if they can't find a medical reason, get allergy tested. If I hadn't known about my allergies, I would have given up on vaping and be back to smoking cigarettes.