Mouth ulcer problem?????

I keep getting mouth ulcers. I am 14 and have had them pretty much since i was seven or eight consistently. They do go away with in a bout a week but about a month later come back again. They are painful and quite big. I have one now. I have tried everything: TCP, Iglu, Salt warm water, salt and bonjela. Please can you give me a way that I can use that will get rid of them fast and prevent them coming back?