Mouth breathing could indeed have some relation, and that's one of the issues that comes up when learning about the Buteyko Breathing Method. They taught us that if we were habitual mouth breathers, to put a little piece of tape over the mouth at night and during the day (not in public), and it trains people to breathe through just their nose.

When I did reduced breathing through my nose years back, it did help a lot to return my breathing to almost normal. That could be something you could try- retraining yourself to be a nose breather.

I remember going through a period some years back where I also had trouble swallowing. I'm not sure what it was exactly; whether psychological or physiological. It just sort of went away and may had to do with my GERD, but not sure.

Have you had any bloodwork done and you know of any nutrient deficiencies?