You should attach pictures for proper assessment.
Do you have any habit which is regular..?
Next Steps
You may have less amount of saliva production which properly needs to be examined by a dentist.
So please visit a nearby dentist.
You can use any Chlorhexidine 0.2% mouthwash by diluting it 1:1 with water twice a day.
Health Tips
If you have any habit then please stop the habit.
Visit a nearby dentist.