Do you have any nasal symptoms? Suggestive of sinus disease?
One of the cause is post nasal drip due to sinus disease.
If you are sure... That is thick saliva.
It might be due to dehydration or excess fluorinated tooth paste or due to salivary gland diseases. Do you have foul smell from mouth ( halitosis)?
Next Steps
A detailed history will help me provide you better guidance and treatment. Consult online
Health Tips
Drink plenty of Luke warm water.
Steam Inhalation