i think you have post nasal drip
from Chronic Sinusitis( Long standing infection and inflammation of Sinuses
), which is the cause of your problem. Try Steam inhalation and warm saline gargling( Add one spoon of common salt to lukewarm water ) and gargle & Antibiotic like Azithromycin
500mg once daily for three days and nasal decongestants may help.
If it does not help please see a ENT Surgeon
Take good care