I have a terrible cough that produces either very little phlegm or a mouth full of watery phlegm. laying down seems to make it worse.?

Possibly reflux: It's possible you are having reflux. Stomach juice can come up from below and cause irritation and inflammation of the throat leading to symptoms that you describe. This is why laying down would make it worse. You can try staying away from acids such as coffee tea and soda, don't eat late at night waiting about three hours before laying down and trying over-the-counter antacid medication.