I Chronic Cough For The Last 16 Years. I Tried

i chronic cough for the last 16 years. I tried every allergy meds, have seen doctors Pulmonologist, immunoligist, GI , ENT's, Psychiarist. tried meds from allergy meds to, anti-anxiety, gabapantin, nothing seems to work.. done a series of test, skin allergy test, positive allergy to all the bushes, pollens and some food, no pet allergy, series of test for my lungs negative, Gi endoscopy -negative, barium swallon negatives
i have post nasal, drip, just white mucous from dripps. the only thing the help my a little is promet/cod6.25
i just take it night it guess it made me sleep, I can not take it during the day .. made me so sleepy just for 5ml. some time I cough even without the nasal drip.. I been taken nexium.. no change . I cough any where even when I was traveling to the different place.. I was prescribe gabapantin the ENT thinks neurological.. but no change