Please answer my question.

I have braces and sometimes they irritate my cheeks by cutting them up. Well the other night while I was asleep I must of kept biting and cutting my mouth. I woke up with swollen cheeks with white on the inside. I looked it up and all I came up with was oral thrush and other diseases, is it possible to develop those over night? I'm hoping theyre just really bad canker soars, can someone please tell me what they think it is? :d