brakes grinding after 3 months

I have a 2002 expedition and the last two times i have had my brakes done they start grinding after 3 months/5000k miles. The first timde was done by midas and the second was by me. Both times were new pads and rotors and im about to have to change them again as you can hear it grinding metal on metal.
Is there something that I could have been leaving out on doing the brakes to make them wear out this fast or do expedition brakes just not last? I do all city driving but ive never had a car go this fast through brakes.
Any help would be appreciated.

Thanks
david

I have my brakes done at Midas also. They last about 30-40k before they need changing. I'll assume that we are talking about the front brakes. They are softer pads than OEM and wear out quicker. They are lifetime pads so you only pay for labor the next time. The grind is most likely from the rotor glazing the pads. You may have a sticking caliper also. When was the last time you changed you brake fluid?
Franco

If you didnt buy a really good set of pads, a big expy will go through them, if the caliper guide sleeves have any wear, the inside pads will wear crooked and fast, rear is very bad for this. cheap organic and cheap semi metallic pads dont last very long and make a ton of dust on your wheels, its best to go with the good lifetime semi metallic on these things and new caliper guide sleeves and bolt kit.