Make sure you check the fuse with a meter. Don't rely on looks. Sometimes they don't appear to be blown, but are. If your turn signals are working, it rules out bulbs, the wiring from the dash to the back, and grounds. Brakes are the same filament. If the third brake light works, it rules out the stoplight switch. If it's not a fuse, it's most likely in the turn signal/hazzard switch.
Edit: As Rubi 4 My Mrs, said the fuse is also the same for all brake lights, so the fuse would not be the issue.