I have a persistant cough that only comes on when i am lying down. i have tried cough syrup, and mucus pills but nothing seems to help

Typically : Typically a cough that occurs from laying down is either from acid in the stomach that refluxes back up into the esophagus and throat causing cough, or from mucous that is a result of allergies that drips from the nose down into the throat while supine, triggering a cough. My advice is to try an anti-acid medication like prilosec, ranitidine, or pepcid, and also take a daily anti-histamine like alavert or claritin (loratadine). Lastly, it is a good idea to follow up with your doctor for this issue. Best of luck.