I get these very frequently and they are quite painful. That looks like a large sore and they usually heal within 2-3 weeks depending on how severe the canker sore is. 2 suggestions for you.. a warm saltwater rinse 2-3 times a day will help relieve pain and avoid acidic foods as they will irritate the sore more. Overall, I don’t think there is any need for you to visit the doctor unless the pain is unbearable. Often they will prescribe cream or a rinse that will relive pain. Just rest up and consider my suggestions, then if the sore is still persistent or getting worse, then it would be wise to visit the doctor.