bulbs keep burning out...HELP!!!

ok heres the deal. my wife has a 99 accord lx 4 door. and it keeps blowing out the left tail light. i've replaced it and replaced it and sometimes it'll work for about 20 minutes or so but then it goes out again. has anyone had this problem before and if so did you fix it? and if so, how? i dont want to take it to the dealership becuase they'll rip me off. and i dont have time to troubleshoot this thing. i could probably figure it out after i've checked everything but i just dont have time. someone please help.....