Well according to Dr. Google, you could have underlying health conditions that could be causing it as well. Dry mouth, liver or kidney disease, autoimmune disorder, etc.

First, the obvious: brush your teeth, floss, and use mouthwash first thing in the morning and before bed. Now, the not so obvious: Buy a tongue scraper, add that to the routine, and make sure you use it all the way at the back of your tongue, too. If you still have your tonsils, you may also have tonsil stones. You can find many videos on how to remove them. I didn't start getting tonsil stones until recently, and I hate them. If there's no improvement, I would try to make a dentist appointment to see if you might be dealing with cavities or not cleaning well enough.

Dopamine