I have a little red dot on my upper lip but its rather not noticable. I put toothpaste on it and it burned. The first time I noticed it was when I went to the dentist to get my teeth whitened and when they put the flouride it burned. I took a look at it in the mirror and you have to lift my lip up a little to see it. I'm scared it might be a cold sore. What could it be?