Talk to Dentist on What Could Be Causing Persistent Bad Breath Despite Good Oral Hygiene?

I have been experiencing persistent bad breath for the past 6 months. This was never an issue for me previously.

I brush my teeth twice a day and regularly use mouthwash and mouth fresheners, but the bad breath continues. My wife frequently notices and complains about it, so it seems to be persistent rather than something I notice myself.

I don't have any obvious dental problems that I'm aware of. I would like to understand what could be causing this, especially since it started relatively recently after never having this issue before.

Could this be due to a dental/gum problem, dry mouth, tonsil stones, acid reflux, sinus issues, or a stomach-related problem? What type of doctor should I see first, and what tests or examinations would be appropriate?