It is important to diagnose what it is.
You dont want to go on diet,buy supplements for months maybe years with out definite answear what causing your symptoms.
You need swap from your tongue and throat.Might be bacterial.
You need good and probably expensive stool test in best lab you can find.Trust me its worth and can save money and time in long term.
For now I would cut all sugars and eat yogurts,kefirs,probiotic supplement,maybe put yogurt on lips like cream.Girls put it on vagina if they catch some fungal/yeast infection.