2006 chevy impala tail lights

my tail  light on the driver side of my 2096
chevy impala isnt working.the brack light
does but while im driving  the light doesnt
work. i have checked the bulbs and  fuses
and they are both still good. its only the
driver side tail light though the light on  the
passenger side works and like i said before
the brake light works on the driver side. so
what could be the problem how do i figure
out  what the problem is and how do i fix it?"