Islandgirl,
Chronic bronchitis is often caused by tobacco smoke. It goes into overdrive and secretes a lot of mucus in the lungs. After quitting, your lungs take quite a while to heal. There's fine hairs in your lungs called cilia that become paralyzed and burnt when you smoke. After you quit, they start working again and their job is to clean your lungs, so the cilia try to wipe the infection out.
Get well soon,
Sylvie, Bilingual Health Educator