PIAA 3 months of life?!

[JOHNSC16V]

I ve been using the PIAA superwhite plasma H4 100/110W for almost 8 month now....oh i forgot said they are different one. you see these light burn out about every 3 months and is killing my wallet. my question is..is this normal?! Is it because over voltage?! If I use normal 55/60w PIAA super white or any other white bulb would that last longer?!
Before i use some cheap 100/110w they burn out ever quicker...so, i switch to the best PIAA and it is still the same....can anybody help me. I try the SEARCH, but nobody seems to talked about this MAX life of these bulb.
thanx =)