I have had this problem since 1995. I carried Anbesol and Kanka even though they were not canker sores. It seems my mouth was always in some state of oral thrush. Finally, the doctor advised Lidocaine Viscous 2%. It works very well and soothes, and gives it a chance to heal. Nystatin (Magic Mouthwash) can be swished and then swallowed, or oral medications like fluconazole can help ease or eliminate mouth sores.
I am on lifelong amoxicillin 3000 mg daily, for a Sepsis infection from 2017 and the oral thrush now comes with that.. The lidocaine is my only help.