I have chronic bad breath and the closest related issue I can pinpoint it to are my sinus problems. My front nostrils are always clear because I can clean those, but deep in the back it feels as if it is perpetually blocked. The only times I can breath clearly are the 5-10 seconds after I sneeze, after which I can breath in through my nose and it feels like the air goes straight to my brain. It's a nice and normal feeling. But shortly after my sinuses always flood back and I have the familiar blocked sensation. I have to breath through my mouth often. It's been like this for as long as I can recall, maybe 15 years. I'm in my upper 20s now. I also think it's been about that long that the wax in my ears changed from dry to a sludgy puss that is now much harder to remove. My sinuses cause dizziness sometimes too. I've tried every mouthwash on the net for my bad breath, and they reduce it from between 20-60%, but none last longer than 30 mins, and absolutely none live up to their claim.
Doctors and my dentist only suggest things I already know and were not of much help. It is evident that halitosis isn't their expertise nor is it something they wanted to brook, and I have the impression medical practitioners downplay this problem because halitosis itself isn't life-threatening. And in truth, it is not. But it's taken a large toll on my life, affecting everything socially to economically. I've lost my job and all of my friends due to it. It is difficult to even hold a conversation with anyone without them backing away.