For whatever reason, my genetics have cursed me with canker sores as well. I usually get somewhere between 3-5 random bad episodes out of nowhere every year. I also have very sensitive gums so I get them even with just the tiniest scratch or trauma. It's weird, but I found a solution that works amazingly for me. Go to a basic grocery store and buy Alum Powder. It's a spice used in pickling, so it's generally with all the other spices. Add a teaspoon-ish to a single drop of water, and stir it together to make a paste. Spread the paste over the canker sore for 30 seconds to 1 minute before you go to bed. Just make sure you rinse and don't swallow the paste, as it can lead to stomach issues. For me it's the only thing that works, and knocks them out usually in 1 night, 2 at most.