Have you been treated for h.pylori? I had an acid reflux caused chronic cough for 4 YEARS before I was treated for h.pylori. It eliminated the cough. I have to stay on Prevacid to keep the cough away, but it only comes back if I go off medication. I've been cough free for 2 years.
If you had an upper GI and they said you don't have h.pylori, don't trust it. You need a blood test. My upper GI tissue test was negative, but my blood test was positive.
My doctor treated me with "Prevpak" which is a corabination of 3 antibiotics and Prevacid that you take twice a day for 2 weeks. I had to repeat the Prevpak twice in 6 month intervals, but after the 3rd treatment my cough is permanently gone as long as I stay on acid reflux meRAB.
I tried generic Prilosec, Prontonix, Nexium, Prilosec OTC and scrip, and one other one. None of these medications work for me. Only Prevacid keeps me cough free. The cough is the ONLY acid reflux symptom I have by the way. No heartburn, no pain, nothing. Just an annoying cough.
Everyone is different, so this may not be the answer for you, but if you haven't already I would talk to your doctor about h.pylori and Prevpak.