Canker sores can be very painful! The exact cause of canker sores is not entirely certain, although several different factors including stress, certain spicy/acidic foods, or vitamin deficiencies can be associated with them. They are also associated with some autoimmune or gastrointestinal conditions such as Crohn's disease or celiac disease.
Canker sores typically resolve within a week or so, although aggravating factors such as spicy foods or mechanical trauma can make them take longer to heal. The fact that your canker sores have persisted for over 3 weeks is an indication that you should return for evaluation with either your dentist
or your oral surgeon
. It is possible that instead of canker sores you have a viral infection (a so-called 'cold sore'). It is also possible that you may have developed a small infection near your initial canker sore. In either case it is important to be evaluated again so that your dentist can make sure nothing has changed since the initial exam. With persistent canker sores, sometimes antibacterial rinses or steroid creams can help them heal. In addition, there are also some topical medications that can be used to help with the pain and discomfort, particularly if this is giving you a hard time with eating. Good luck, and please see your doctor