1991 Chevrolet Cavalier brake problems

You gotta include some details. What was done with the rotors? Did you torque the lug nuts? Did you lubricate the caliper slides? Did you prepare the new pads or did they come prepared? Any chance the linings or rotors got contaminated with grease? Have the steering and suspension systems been inspected for worn parts? Where do you feel or see the shaking?

There's quite a bit more involved in a professional brake job than just hanging new pads or shoes. Mechanics do a number of things to avoid noises and vibrations from occurring, and there's things we can accidentally do to cause them. If the rotors weren't machined to make them match the new linings, there's no way to know if grease or other contaminants got involved or what else might have happened. The affected brakes need to be disassembled and inspected to see what is causing the vibration. A mechanic will know what to look for.