Do I have a cavity?

Usually I’m really good about brushing & flossing. However, yesterday, I got really lazy—I did not brush in the morning or night, and fell right asleep. I woke up at around 6 A.M. and panicked. Immediately, I brushed & flossed. However, when I brush, one tooth hurts a lot. I also have braces. Is this a sign of a cavity? What are other risk factors? Should I be worried? I really hate myself now!