These ulcers are known as aphthous ulcers and they are recurrent. They may be exacerbated by biting or stress. Unfortunately, there is nothing like a quick remedy.
First of all, avoid stressful situations. You can apply mucopain gel to the ulcer five minutes before food. Multivitamins may not have a direct benefit.
Next Steps
These ulcers usually resolve in a week's time. If they last longer or are quite large, Pl consult a dentist or Oral Medicine specialist. Other medicines may be prescribed.