Acid reflux. Try taking a tums when you are about to lay down.

I am sorry you are struggling with this and I can certainly understand the frustration. I wish there is an easy and straightforward explanation, but, unfortunately, cough is a complicated symptom which could arise from variety of underlying issues. Allergies (especially seasonal) can be a trigger, silent reflux disease, post nasal drip, even a type of asthma called cough variant can present that way. I would suggest seeing either your PCP or an allergist for full evaluation and proper medication suggestions.
Hope that helps.

Sincerely,

Monika Korff, MD

Cough with lying down to sleep is most often acid reflux. The usual pattern is that it starts as soon as you lie down. Sometimes a chronic sinus infection can cause a wet cough with lying down. Asthma can also cause a cough when a person is in bed, but it usually does not start right away and instead starts in the early morning hours like around 1 or 2 AM. The symptom you have is thus most likely acid reflux. You can try over-the-counter famotidine (pepcid) 20mg or 40mg after dinner and see if that clears it up.

Alan E. Gorenberg, MD