The same thing happens to me! I've attempted oil pulling a couple of times and always stop when I feel I'm starting to get a canker sore. This time, though, it occurred to me that it might be my body's way of getting rid of this awful infection my dentist said I have. I'm determined to kill it with oil pulling with coconut and oregano oil, brushing with coconut oil and baking soda, swishing with Colloidal Silver and also with peppermint oil!