Do both pads wear evenly? If so, do you drive with 2 feet? If so, stop doing that. It doesn't take much movement of the brake pedal to cause the pads to contact the rotor and wear them down.
If one pad wears more than the other, then it is likely a hanging caliper.
Either of the above may cause overheated rotors that will give you another symptom. After driving a while, especially at hwy speed, when you apply the brakes, does the steering wheel shake?
If none of the above, how many miles between replacement and what is your city vs hwy driving ratio?
Typically, you should get at least 50,000 miles on a set of pads depending on the size and type of vehicle. A hybrid might go 150,000 or more.
Another question, why are you replacing pads, and who is doing it? It is very common for service shops to tell you you need new brakes when you do not. It is their cash cow and is easy to sell to uninformed customers.