I found triggers for my canker sores (beyond stress.) Specific foods – pineapple, too much dairy, chocolate or sugar, ANY dental work – even just cleaning and a few others.
I have a "big" tool in my arsenal now – when I get a major outbreak, I take Acyclovir, a prescription, for 5 days. My primary prescribed it to keep on hand. It's not a cure, but seems I need it 2-3 times a year, and it calms things down a great deal so I may go weeks before any new sores come.
By the way – this seems to be a family thing – some of my siblings get these too, as well as my daughter.