I have had this problem for the past 3 years. I need to see if you can help...

After a few hours of sleep, I feel there is build up of saliva and when I spit it is yellowish  then I dont caugh but force my spit out from my noise to my throat and I see yellowish greenish sputum

During day I dont have any symptoms, no caugh or snezzing either. 

any idea,,,,,----