This could be due to post nasal drip which is mucus accumulation in the back of the nose and throat, excessive or thick
secretions, or impairment in the normal clearance of mucus
from the nose and throat. Try to avoid the nasal irritants such as cigarette smoke, perfume, aerosol sprays, smoke, smog and car exhaust. If it persists, it is best that you have this checked by your doctor for proper evaluation. Take care and regards.