What Is The Possible Cause Of A Yellow Tongue When

What is the possible cause of a yellow tongue when I eat something with sugar content? Have tried two anti-fungal meds., clotrimezole tablets, and 2 oral fluconazole scripts (6 pills each) to no avail. Could this be a serious issue! Really has me concerned. GP does not seem to have a clue. ENT Doctor prescribed clotrimezole, GI doctor tried the fluconazole. Had full bloodwork-up 2/18, everything was normal except low Vitamin D??