Thanks for asking the query,
Canker sore can occur due to trauma physical or chemical or even due to stress.
I would suggest you to visit to a Dentist
and get the checkup done.
Take warm saline gargles 3-4 times a day to give a soothing effect.
Apply Dologel oral ointment or mucopain topically over the affected area.
Avoid eating of hot and spicy foodstuffs for some days.
Take multivitamin tablets.
Relief stress if any, relax and take complete rest for 2-3 days.
Maintain a good oral hygiene
, use antiseptic mouthwash gargles like chlorhexidine
mouthwash twice daily to prevent superinfection
and promote healing.
Hope this helps out.