I have asthma with an elevated mucus component. My pulmonologist says this is a common asthma symptom and it seems to wax and wane seasonally for me. I’ve also had X-rays, CT scans and they are all clear. Additionally, your smoking history seems relatively low when translated into pack-years. And after stopping smoking, it can take your lungs a long time to recover and settle. You may need to be more patient.