Considering, you are not undergoing medication for a long time. Because as a side effect some medications show side effect of dryness of mouth.
Hope no h/o salivary glands infection or operation,trauma to head and neck region.
No H/ arthritic problem, as it sometimes Co exists with salivary glands disorder.
If alcoholic for a long time that may reduce salivary flow. So, quit that habit, if exists.
Consume citrus food as much as possible.
Continue drinking water 2.5 litre per day, little by little.
Sugar free chewing gum/lozenges.
Next Steps
visit dentist for clinical examination.