It sounds more like a cold sore.
Canker sores and cold sores are often confused.
Info found:
"Cold sores typically appear outside the mouth -- usually under the nose, around the lips, or under the chin, while canker sores occur inside the mouth.
The exact cause of most canker sores is unknown. Stress or tissue injury is thought to be the cause of simple canker sores. Certain foods -- including citrus or acidic fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes, and strawberries) -- can trigger a canker sore or make the problem worse. Sometimes a sharp tooth surface or dental appliance, such as braces or ill-fitting dentures, might also trigger canker sores.
Some cases of complex canker sores are caused by an underlying health condition, such as an impaired immune system; nutritional problems, such as vitamin B-12, zinc, folic acid, or iron deficiency; and gastrointestinal tract disease, such as Celiac disease and Crohn's disease.
Cold sores, also called a fever blister or herpes simplex type 1, are groups of painful, fluid-filled blisters. Unlike canker sores, cold sores are caused by a virus and are extremely contagious. "
See if some Abreva helps.
You should be able to find it in any pharmacy.
Talk to the pharmacist and see what they recommend.