I have a bad taste mostly when i cough...

Hello. I came here cuz for more than 2 months now i have a bad taste on my mouth that i dont know what it is.
Firstly i thought it could be a bad tooth or something so i went to a dentist and fixed all my teeth.
For one day i didnt have a bad taste at all.
But the day after it began again.
Its like something rotten or i dont know exactly. And i mostly taste it when i cough.
Might be comming from the pneumonia.
I am 18 years old smoking since 16.
Im not drinking too much booze.

Please if you know what i have also help me to solve it.

Kind Regards,
Jim Bakopoulos