Hello~It sounds to me like you have a Candida infection called Oral Thrush.
Oral thrush is a yeast infection of the inside of the mouth. Its main symptom is the appearance of creamy white spots on the tongue or insides of the cheeks. Oral thrush can cause discomfort but is not usually a serious condition. Treatment options include warm salt water mouth rinses and pharmacy medications.
Oral thrush and other yeast infections are caused by an overgrowth of the fungus Candida albicans (C. albicans). ... You may develop an overgrowth of C. albicans that causes oral thrush if you take certain medications that reduce the number of friendly microorganisms in your body, such as antibiotics.
Here is a link: https://www.medicinenet.com/thrush/article.htm
There is a lot of info on the net about this and other Candida issues. I would certainly talk to your dentist and see if he/she has any ideas on how to help.
In the meantime, I would avoid all wheat products, yeast and sugar as Candida thrives on these foods.