How can you get rid of / avoid getting canker sores?

I have 3 canker sores on the inner right side of my lip, 3 on my upper right gum line (like above my teeth), and one on the bottom part of my mouth, like the pink, mushy part. And I might be getting another one on the right side of my tongue!!! =( They all hurt really bad and Idk why I've been getting them. My mum says it's cause of stress but I really haven't been stressed lately, so Idk what's going on. How do canker sores form, what can you do to get rid of them quickly, and how can you avoid getting them at all? Help!