The thrush creature (much nicer name than fungus) is yeast and it thrives on starch and sugar. Limit your eating of sweets and starches and rinse and brush after EVERY meal or treat. Beyond that Nystatin worked well for me.

Mark, 21 Year survivor, SCC right tonsil, 3 nodes positive, one with extra-capsular spread. I never asked what stage (would have scared me anyway) Right side tonsillectomy, radical neck dissection right side, maximum radiation to both sides, no chemo, no PEG, age 40 when diagnosed.