Dry throat white tongue. Nystatin given no clear up. Dr said not thrush. What is it?

Need lab work. If you want to know for sure, then you will need a biopsy of the site. Some dentists will do this. Oral surgeons, general physicians, ENT referral----do not give up !
Unsure. Thrush would be the first thing i would think of. These things are hard to tell without seeing you. There are some medical issues such as diabetes i would be checking. Did your doctor look at it or test it?