no brake lights???

hi, i have a citroen picasso and i cant seem to get my brake lights to work. I first checked the fuse which was fine and then got a brake switch and changed it which sorted my problem out, but unfortunately just for one day!! so presumed the switch was faulty and returned it and had it replaced. Great they worked again, but , only for the day ! its baffled me. The first time i took the switch back i checked my bulbs and they had blown, so they have been replaced too, has anyone got any ideas why they dont last longer than a day? please!