1995 Hyundai Accent Brakes are squeaking / lurching

I obtained a 1995 Hyundai Accent Hatchback a year ago. It sat on my driveway for about 4 months, and when I started to drive it I noticed the brakes were rusted and made a horrible noise while braking.

I brought my car in to have all the brakes / rotors replaced. After about 2 or 3 months of driving it, I noticed that the front brakes are making squeaking and sometimes clunking noises, even when the brake pedal isn't depressed. When I do press my break, I feel a distinct lurching every time the wheel goes around, as well as my break pedal bobbing up and down as the wheels rotate.

I believe the rotor is likely warped, but I am more wondering what could have caused this to happen after 4 months of replacing the rotors? I don't want to spend another $600 to replace to brakes to have this happen again in a few months.

Thanks for your advice