no drivers side brake light? HELP ME PLEASE

Hi to anybody out there who has any advise on my lighting (or lack there of) problem,

The drivers side rear brake light will not illuminate when the brake pedal is compressed.
The passenger side one does.

I have tried:

1. swapping out for a new bulb
2. putting the passenger side bulb in the drivers side
3. checked the fuse box
4. the running lights, turn signals, and hazards all work fine

I have no idea what is going on here. Any help out there???