So Finding this thread, I too have a constant post nasal drip, and cough (constant phlegm in the lungs) from what I believe is caused by the covid vaccine,... and it drives me and family members nuts... though it does seem to be better than the alternative of having all the phlegm dry up to a solid mass thereby making it impossible to breathe. I tried Mucinex pre covid and it helped, but now the sheer volume increase of phlegm has me concerned at the possible danger of not being able to breathe if i try Mucinex again. I am concerned, and will try to reduce sugar intake, but i am also glad that i am not alone in this matter. I just hope places like the Mayo Clinic will not just brush this off with an "Its fine, it will just go away statement". I've been dealing with this added constant phlegm for over a year now, and am sad that the vaccine that may have saved my life will now shorten it due to these irritating side effects.