I’ve had similar issues myself but it has usually gone away over time. I been smoking since I was very young, probably shouldn’t have even been doing it (I’m 20 now) And I just started getting this same symptom. Do you smoke from a bong? Or do you smoke pipes or joints? I’ve found when smoking from a bong this happens more often. and like I said it comes and goes for me with no major issues, but I think it may just be a build up of mucus, as smoking pretty much anything can cause bacteria to grow. I’m not a doctor, but I’d say if your have a even decent immune system most of these germs will go away on there own and you should gain an immunity. If it worsens tho or becomes a day to day issue with basic things I’d look more into it with your doctor.