My molars hurt when i drink something cold or breathe in?

It could be a cavity, but chances are small that it is a cavity big enough to cause these symptoms. If you just got braces, then your orthodontist must have checked for cavities before he put the braces on. It could be a case of receding gums. This happens to a lot of people. Just use a sensodyne toothpaste and see if it gets better. If not, then talk to your ortho about it the next time you go in.