What Is This In My Mouth?

I'd go check in with a doctor. My kids had this once and I can't remember what he called it. It turned out it was something relatively common and easy to cure, but be sure not to share a drink or eating utensils with anyone else and don't kiss anyone!!! Thrush is more of a yeast infection at in the mouth.. so it doesn't sound like that. Canker sores aren't clear. So go see the doctor.