For a while now i have experienced this. I will get a really bad taste in my mouth and it won't go away despite how much I brush my teeth or what I eat. I have come to realize this all started and is caused by this greenish substance that is in the back of my mouth. It is a green white and collects in the back of my mouth/throat right next to my uvula. Before to try to fix this problem before I scraped the substance off. That's when i realized that the substance was the cause for the bad taste because it reaked. It comes back after a while and doesn't stop. I just want to know what is going on and why? And how can I stop it?