spitting problem

For the last 2 years, i have been suffering from spitting problem. I do smoke and i have problem of cold. My main problem is that i spit too much. When i am outside of the home i spit more. This problem is greatly disturbing my everyday life. Even now a days i am afraid of going outside of my home for having spitting problem. I also face spit problem when i am at home but the rate of spiting is less when i am at home. Sometimes i feel that the inner skin off my mouth has became thicker and then i drink water to refresh my mouth but it doesn't work much. I have consulted with a doctor about my diseases but the doctor said that spitting is not a disease at all. But the fact is that i m really suffering from this problem. It seems to me that i will never get rid of this problem. I am becoming depressed. Can you give any suggestion please? please note that it is normal spitting problem not cough problem