I'm in the same boat as you. I'm 22, with the same symptoms, same experiences.
I've seen ENTs, had a CT scan, nothing wrong with my nose according to multiple ENTs. I've tried a lot of 'home remedies' which mostly turn out to be useless quack treatments. My latest thing i'm trying is Oil of Oregano because I have read that some people had success with it.
I'm on day 4 of using it - drinking it in water and also putting a drop in my neti pot. So far it has had absolutely no effect on my symptoms.
I currently work in a customer service role and I must get through about 5 packets of gum per shift. I try and stay positive about my symptoms but on especially bad days where I can taste my bad breath and someone asks if i can smell that too that really ***** and brings me down.
Just made an account to reply to your post to let you know i'm in a similar situation to you and one day we will be cured.
I had a similar problem for almost 10 years. I kept getting the same treatments, with my dentists always prasing my strong teeth. I switched dentists about a year ago and the new dentist discovered a crack in one of my molars. The tooth had rotted and caused petrified fluids to drain through my nasal cavities. After the too extraction, e bad breath disappeared.