your brake / tail lights are dual filament lamps. so if your brake lights are working, then chances are the 2nd filament has blown in both ( unusual )
Could be as easy as swapping out the lamps.
It could also be a fuse for the tail lights, worth checking that too...
But i would have thought something else not be working if the fuse was blown...
Yes there is a fuse to control them, but I can't remember if its in the drivers side dash fuse box, just to the left of your knee, or in the engine bay fuse box.
both have diagrams on the inside of the lids, take a peek .. and if blown swap out for a new fuse.
Hope that fixes it for you..