Unregistered

Hello, I recently bought a used '03 Mustang last September, which is also my first Mustang. I have had a few cars before and done all my own work on them for the most part, and never really had any trouble like I'm having now.
The car has been making a squeaking noise from the start, I took it in and was told the axle is bent, so no biggie, a lot of cars have this problem I think. In January I started to hear a bad grinding noise coming from the brakes, it simply sounded horrible going at low speeds, it sounds like the car is about to fall apart. I replaced the pads and rotors on all the wheels and they were worn down pretty good. Here it is the beginning of April and the grinding noise is coming back and it's pretty bad. My question, could this just be a lemon car, could the axle have anything to do with the brakes wearing out so fast like causing uneven wear or something. Could it be the calipers aswell or just bad brakes? Or is this just a common Mustang problem?
Any help would be appreciated greatly.