Whats wrong with my brakes?

i drive a 1998 ford contour gl. When i press on the brake the car, and the pedal are very jerky, like i can feel a pretty hard tap in my foot. it also makes the car shake. It doesn't make any weird sounds or screeching but im not exactly sure what it could be. the car has brand new pads and rotors, so could it possibly be the caliper? i just need some help to figure out what it could be so i can fix the car and get it back on the road safely.