A couple of things come to mind. First, the rotors may be too thin. A rotor has two sides. Sometimes the rotor can measure to be in tolerance but if one side is worn thinner than the other, it can cause it to warp very easily. Get someone to measure the width of the rotor on both sides and they should be close to the same. If not, replace the rotor. Cheap pads could be a culprit.
Edgewood Auto Parts #253, Edgewood, Texas