Probably its an ulcer.
Causes might b history of fever in recent past, mental stress, trauma, etc
Can continue with zytee or Dologel-CT.
Lukewarm salt water or mouthwash acn also b used.
Should b healed within a week. If not, consult a dentist.
Next Steps
Consult a dentist.
Health Tips
Avoid consumption of hot beverages until the ulcer heals.