I'm quite prone to them when I'm tired, unwell or haven't been looking after myself with diet etc. I have a horrible one at the moment and it's so sore. Aside from the localised pain it gives me a horrific headache, swollen glands and I just generally feel tired and unwell.
Looking at it you wouldn't believe such a small thing could cause so much discomfort. Is that what ulcers are like on other parts of the body?
I've tried every treatment going and while some mouthwashes do help a bit, it's usually just a waiting game until the pain eases and it eventually disappears.