Update: facial tightness still persists after trying several things (diet changes, physio, chiro, acupuncture, etc), so finally saw a neurologist about it He ordered a new MRI as the old one wasn't detailed enough to see what was going on with the trigeminal nerve.

New MRI suggests a vascular loop touching the trigeminal is the cause. As I'm now so used to the symptoms (and generally don't even notice it anymore unless I focus on it) and it's not stopping me from doing anything, I'm just going to leave it be and cross fingers that it doesn't worsen or develop into neuralgia in the future!