abs brakes prevent stopping, peddle pushes back allowing forARD MOTION , AFTER few seconds of pushing harder on the peddlle ,very hard ,brajks apply

I replaced my brakes and my left front, which is ABS, suddenly decided to turn itself on constantly, i took it to my mechanic and they say they have no idea whats wrong, but it seems to me the AS is constantly on, because when i brae, it pushes back on me. if anyone can give me any ideas, or maybe just give me a damn solution hah. i would appreciate it more then i cold tell ya.

The anti-lock brakes are always on and the light is on most of the time. When you go to stop, the brake pedal starts to vibrate and it won't stop. Please help me with this problem