Air Brake Disc Pads problems of the 2004 Nissan Armada

Car began shaking when brakes applied at 13,000 miles. Called dealer to see if this was uncommon or if other Armada drivers were complaining and told they knew of no problem. Took car into local auto store and was told the rotors were bad and to take back to the dealer since it was not common for this to happen so early. Dealership turned rotors. Same problem occurred 3000 miles later and brought back to dealer and asked for rotors not to be turned, but to fix the problem. They just turned the rotors again. Seems they are just putting a bandaid until I have to pay for the problem myself. I have kids and feel very unsafe. I am ready to bring it in again because the car is shaking again. I have other issues, but they are just bothersome. This brake problem scares me and it is expensive to keep fixing this when it is out of warranty. Help!!!!.