I have the same issue. It started last month and I had two of them on the tip and they went away after 3 to 4 days with no pain. This month, just this past weekend, they showed up Friday night and went away by Sunday night. Though, the first thing that went to my mind was Herpes which freaked me out really bad. But, it doesn't seem likely since, at least for me, they went away quickly with no pain and they did not look like what I have seen pictures of online. I don't have the money to get tested for that yet to know for sure.
I also have ulcerative colitis so I'm still trying to figure out if that might be a cause too. I did read too that some people suck and push their tongue into their teeth while they sleep. I had braces so most of my teeth are straight except for the bottom tooth right in the middle where it jets backwards towards my tongue from my wisdom teeth coming in. The sores I had developed around that tooth, so again, not sure if that would cause it either.
How long does yours last? Have you been tested for herpes? Got crooked teeth? =P