It is difficult to give a definitive diagnosis as the history you are giving is incomplete.. but by any chance if u have a dry mouth then you should take lots of fluid.an oral swab or biopsy can be done to check for thrush(fungal infection) which can be treated with antifungal medication.Any sharp teeth or broken filling should be removed.Also try eliminating mouth wash, tobacco, coffee or any acidic liquid in use for two weeks and check whether it helps.certainly the correct treatment can only be suggested after an oral examination.

Could be due to deficiency of vitamins,any habits, any auto immune disorder...better see a doctor