I think I figured it out; Apthous Ulcers.I had them. Nothing to worry about, probably caused by stress. They hurt for a few days but they go away. Not contagious.Good luck!
I know its
http://www.medhelp.org/posts/new/1529770#been a while but did you ever find out what it was? I have one that looks verrry similar.
could be a possible canker sore,herpes,(This pattern has important implications for the many people who fear they have herpes but don't: If something lasts for weeks, it is unlikely to be herpes) or you could have just hit the roof of mouth while eating and cause a bruise.
seeing a dentist is advised, if it is a some kind of sore/infection it could turn alot worse if left untreated