What causes sores on the tongue?

Can't be sure. : What have you done to it? Taken? Had to drink? Had to eat? Need lots more information to guess at your particular concern. See your dentist for an evaluation.

Lots of things: See your general dentist or an oral surgeon when you have these sores present for a definitive diagnosis. The diagnosis will determine the cause, if known (for some types of sores, the cause is not well understood).

Many causes: Meds, supplements, acidic foods, grinding and consistent biting of the tongue, vitamin deficiency (b12, ) nutritional allergies and other allergies. I would possibly keep some sort of diary and try and note what you were doing or eating when there is an outbreak of the sores. If the sores remain, go see a dentist asap.