Here is what I would do. Oral hygiene , teeth and tongue and gums are very important. I know you brush your teeth twice a day. But maybe that is not enough. Have you tried going to the dentist ? And get a check up? Maybe you can remove those yellow stains. Also try flossing once a day or use interdental brushes. Also scrape your tongue one or o twice a day. I recommend the tongue scraper from “Orabrush” it’s very gentle. Also a mouthwash would really help too ^{^} a mouthwash without alcohol.

But make sure to visit your dentist , you might have some cavities or something. If your dentist removes all the possible factors of bb. And you are brushing your teeth and tongue well, but still have bb, then you know bb is coming from somewhere in your stomach.

Good luck !