Hello, you can apply baking soda over it or do baking soda in water mouth rinses. This will help to heal your ulcers. If they still persist, you need to consult a physician and get your vitamin B levels checked. If required take supplements for it.

What you are suffering from is recurrent apthous stomatitis. It is usually due to immunological problems. People who are usually stressed face more of such issues. There could be associated gastroenterological symptoms. Get a vitamin B12 level and folate level checked. Try to consume less junk food and eat lots of fresh fruits and vegetables daily. Include curd in your diet regularly. Intake of lot of fluids. Exercise regularly. Avoid constipation. And use a toothpaste which is free of foaming agents.