Do you happen to have bifid uvula? That little punching bag in the back of your throat is cleft? This could indicate soft palate malformation that often goes undetected but harbors food and bacteria and can cause many allergies, sinus infections and odors. Gargle salt water vigorously every night the last thing before bed until any bits are rinsed away. Consider a nasal lavage system, easy peasy, you don't have to spend money - use an empty well-washed squirt detergent bottle with the nozzly top, the purest water you've got (boil, cool) and a bit of salt.
OR you should know that not all infections of teeth are detectable because sometimes there is nerve death. You could have a very serious dental issue and not even know it. Does one cheekbone sometimes get red? Do you sometimes get flares of the lymph nodes down one side of your body? This is a clue. If you do not see a dentist regularly, get checked out at a clinic right away.
These are two less considered possibilities.