I have had them periodically all my life. Last spring I had one me that was on the mend(didn't hurt that much anymore) when I had dentist check up. The dentist told me that I need to come back in two weeks to rule out any nasties. I went back and the ulcer had healed. Now I got one again and felt really nervous for the duration of it which was two weeks.
I wonder how you can avoid getting them. Before I didn't give a second thought as they came and went.