Mouth ulcers aka Aphthous ulcers could be caused due to multiple reasons mainly being stress or multivitamin deficiencies.
Thought only symptomatic relief can be obtained with topical management, the core reason has to be evaluated.
Next Steps
Can consult a dentist or a Maxillofacial surgeon for opinion and clinical evaluation
Health Tips
Work on your environment and try to be less stressful. Have a good nutritious diet.
You can try Betadine gargles for temporary relief.