I used to suffer from canker sores quite a bit. As any canker sore suffer knows, they are painful suckers because it's impossible not to keep your mouth immobile (eat, talk, etc.). All the over-the-counter medication never worked because the inside of the mouth is hard to coat. Healing usually took 1 to 2 weeks no matter what I put on it. I got a tip from some website long ago about how canker sores came from your own immune system attacking itself b/c of trauma to the mouth. It suggested not eating potatoe chips because it can nick your mouth tissue. It actually works. AVOID EATING CHIPS AT ALL COST.
Try Kaopectate to coat and soothe after using an OTC mouth rinse recommended by my son's pediatric dentist called, dang I forget but it's like Pedia something or rather (oral antiseptic rinse) in the dental aisle of the drugstore in a white bottle. The rinse is an antiseptic and comes in a white bottle w/blue lettering and usually on lower shelves and to allow the canker sore heal faster. The Kaopectate will coat the open stinging wound when it acts up.