@celia16 Your own doctor or another physician would refer you to a pulmonologist. Other countries call that specialist, a respirologist. You could ask your own family physician for a CT scan of your lungs.

We do need to be good advocates for ourselves because diagnosis can be tricky. That said, don’t read too much on Google. The testing will help determine if there is anything that needs further attention.
You can be tested for allergies too.
If you have an ongoing cough and mucus, I wouldn’t hesitate to request a CT scan and referral.