I can only speak for myself, but GERD had definitely caused my cough for many years. I recently had the Nissen Fundoplication, and my cough has improved tremendously. My cough was more asthma related, but I do know that GERD can cause irritation to the esophagus, bronchial tubes, and vocal chords. The fact that its worse when you lay down at night, is even more evidence that it might be GERD related.
Best wishes in getting to the bottom of your problem,