Seeing an oral medicine or Orofacial pain specialist is advised.
It could be a canker sore that has developed as a reaction to either a food, lack of sleep, stress, or another unknown reason. I'd have it checked for sure asap. Oral cancer quite often first presents itself on the lateral (side) tongue so you want to rule this out. It may be something as harmless as a canker sore though so don't worry.