Please, somebody help

25 years ago, I was spitting mucus without having a cold. Tests in Quebec using air tight volumes indicated COPD. Four years ago, in New Brunswick, a spirometry test indicated "no COPD." And no explanation about 20 years of producing mucus. Then, about 6 months ago, another spirometry test was concluded as "no COPD." So, why do I keep producing that much mucus?