I had a chronic sinus infection that lasted years. The ENT had me take antibiotics a few times, which cured the symptoms, but the y came back a week or so later. He even did sinus surgery to open the passages. The infections didn't go away. Then he said I didn't have an infection and sent me to a neurologist who had me get a CT scan which clearly showed a full sinus, so more antibiotics. And it came back and back and back.
I finally gave up and started doing sinus washes. I read about sinus plaques - infection covered with gunk that didn't clear easily. My allergist had me try her formula for making a rinse with an antibiotic. It didn't work. I had to try to dissolve a thing that was very waxy in my bottle. It didn't dissolve enough to get anything into the sinuses. As I said before, it's hard to get anything into the sinuses because blood flow is minimal. The normal passages or drainage outlets are tiny too. By the way, the sinuses in the middle, by the cheek bones, open upward. You have to tip your head upside down for them to drain.
I had a surgery that had me on IV antibiotics which got rid of the infection for a while, but it came back after a few weeks. I just kept up with twice a day washes and eventually the sinuses cleared.
I haven't had a bad infection in a couple of years now, but I do the washes when I get congested. I don't want to get a plaque buildup settled in again.
I think, my opinion only, that doctors get tired of not being able to cure us quickly. Medicine is not perfect and doctors are human. The patient has to think and participate in the cure too.
I recommend looking up terms like sinus plaque and see if there are any new treatments which you might suggest, gently, to your doctor(s). If one doctor gets tired of you coming back and back and back, go to another one as I did. If an ENT cant fix you try an allergist.