I Have Had Constant Cough For Over A Year. It

I have had constant cough for over a year. It is often a dry cough, but at night when I lay down it will produce some phlegm. I do have some back pain, but my doctor has detected some deterioration in my spine around the T-3, T-4 area. There have been tests to rule out things, such as an EKG, Pulmonary function test, and Allergy testing. I have tried an inhaler to see if it was non-infectious bronchitis, Claritin or other types of allergy medicine, and acid reflux medicine. I have been seeing I chiropractor to loosen up the spine and see if I get any relief. Nothing much yet. I still have the cough. How would you suggest to proceed? It is still an annoyance. Please help! Karen