Hi..
Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concerns..
As per your complain Oral yeast infection occurs due to fungus Candida Albicans and is commonly related to low immunity or compromised immunity..
Other causes can be 
dry mouth, intake of antibiotics and steroids, Oral contraceptives etc..
So as you are having repeated episodes of the same problem it will be better to first of all get a complete body investigation done like complete blood picture, Oral swab etc to rule out the cause for recurring Thrush..
As of now you can restart 
Nystatin mouthwash  gargle, 
Clotrimazole lozenges and Oral medication like 
Fluconazole, 
Itraconazole etc after consulting a local Physician...
Take plenty of Probiotics like Yogurt and garlic..
Hope this information helps..
Thanks and regards.
Dr.Honey Nandwani Arora..