Thanks for the query.
The causes of mouth ulcers are stress, vitamin deficiencies, smoking, alcohol, infections and poor oral hygiene since you have the issue for 20 days, it cannot be left unattended. You will have to consult a dentist and get it examined and treated accordingly. Meanwhile, you can use metronidazole gel for local application and betadine mouthwashes after every meal and also drink plenty of water. Oral vitamin supplements of Vitamin B and zinc will help you.
Hope this helped.
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