For non-cyclists: brake pads have a minimum thickness, and usually a wear line molded in (less common on disc brakes). If you've got enough pad material and it isn't glazed or contaminated, it isn't time to change them yet. They can last years. I've got maybe 6,000 miles on the pads on my road bike, and they're fine.

The only normal case for needing to change pads every couple months that I've run across is people riding lift-service downhill. In which case, buy a set of digital calipers and check your rotors regularly, because they have a minimum thickness too.

For reference: I am a bike mechanic, though not a paid one at the moment.