I had the same problem. Cough only when I lay down. Mine was a tickle or pick in my throat as I like to call it, and it would make me cough. My doctor put me on Zyrtec once a day and it cleared it right up. Also clareting over the counter is also good for post nasal drip and allergy related stuff. Just remember clareting and Zyrtec are melds that you have to take once a day as scheduled to see benefits. You can't take it just when you need it. Doesn't work that way. If you smoke. Stop smoking. I hope this helps. Also I don't know what kind of doctor your seeing, but if what I suggested doesn't clear the problem. Go to a ear, nose, and throat specialist.