Why have I constantly spit loogies since I was 14?

I have spit all the time. In the morning, after a meal or drink, after a cigarette when I go to bed. This is not a joke. I have been to the doctor but he didn't know what it was. I have also tried to research this on the internet and I can't find anything on it. I was spitting before I started smoking. Could it be my tonsils? Nobody seems to know what kind of disease this is. It is actually mucus that I spit out, not regular saliva.