Hello, My Boyfriend Has Had This Sore Under His Tongue

Hello, my boyfriend has had this sore under his tongue on his frenulum. He noticed it the day after he gave me oral. It is kind of white and patchy but not bad. It isn't painful but we both think it is a canker sore, but he is worried. We have never had sex, just oral and we've done it a lot. I had a yeast infection two weeks ago but I feel perfectly fine and nothing has happened to me about a little over a week. He thinks it could possibly be because of my yeast infection. Could it be? Do you know what this is? Is it just a canker sore? How long will it be there for? Please let me know. Thanks.