A few weeks ago I had a touch of laryngitis and gargled with the usual salt water, etc. to kill the bad throat bugs. Unfortunately, it also killed the good throat bugs which are necessary to keep your mouth and throat healthy.
This allowed the flora in the mouth to grow wild and, according to the Doctor, finished up as oral thrush.
It eventually took two bottles of Nystatin to clear it and later I also started to rinse my mouth occasionally with a strong solution of bi-carbonate of soda which I believe kept the mouth flora under control until the good bugs got re-established.
My tongue has always been a bit yellowish but is now a nice normal pinky colour.
Just thought this might help.