Candida infections do occur in the mouth but only in a small percentage of cases. The white coating on the tongue is tongue plaque made up of bacteria, mucus, sulphur compounds, and food debris.
If you have an increased collection of nasal mucus then quite commonly the coating is on the back third of the tongue at or past the gag reflex.
The coating is a symptom of bad breath, and should be cleaned with a tongue cleaner and bad breath products.