Have you had dental work such as a root canal done in that area?
I hope that you have an answer by now. If not, I have a question: your ENT only looked up your nose with a special camera? My ENT looked up my nose with a special camera and sent me to have a special MRI. Regular MRIs done at a hospital often miss things related to the sinuses. I suffered for years with chronic sinus infections without the coughing and sinus discharge. Actually, I was born with part of the problem; the rest I developed later. My primary care physicians (several over the years) thought they could fix me by prescribing drugs for me. Eventually, I finally was allowed a referral to an ENT. Turns out I had several problesm. I have had several surgeries to correct what they can correct. I am glad that I had them.
If you don't have the answers you need by now, get the opinion of a second ENT. I pretty much had the same symptoms you had, but my doctor would not refer me to an ENT until I demanded a sleep apnea test. The sleep doctor insisted I get a referral to an ENT. I was born with OSA and with some abnormalities in my nose and sinuses. I wasn't diagnosed until 54 years after the onset of the initial problems and about 20 years after the onset of the new problems. In addition, it is possible that you have developed neurological problems.