Fuses keep blowing ?

I have a Gilera runner vx 125 55plate and basically the brake lights weren't functioning properly, so my friend like an idiot put a metal screw driver into the little hole where the bulb fits in, and then touched the metal inside and blew something, at first we thought it was the fuse but now when I change the fuses, it just keeps blowing the fuses one by one every single time, would you know what it wrong with the bike ?