Based on the history given of recurrent oral ulcers it could be
vitamin deficiency which on oral multivitamins shall subside within a week or two.
It would be advisable to visit your doctor if it does not respond to oral multivitamins.
Next Steps
avoid spicy and hot food until these ulcers are active
Health Tips
multiple ulcers not responding might also be of viral cause .so do visit your doctor on non responsive ulcers