I've been having pain in my upper jaws and teeth. it's not severe and it seems to come and go. could it just be sinus or something else? no fever, no cough or stuffiness. i do wear a mouth guard for bruxism. thank you?

Could be sinus involvement or some type of mild neurological condition. Do you always wear your mouth guard, as advised. If condition worsens, or if you would like more piece of mind, start keeping a journal of when problem occurs, and then address Neurologist/ Oral Surgeon.

There are many things that could cause pain in that area, mostly related to the teeth or to the jaw or sinuses. If the pain results on its own, it is probably nothing to worry about, but if it persists or worsens, you should see your dentist or your primary care doctor. Good luck.