i changed my rotors and the mechanic didnt change the breaks, and like a month after that service when im drivinga on a highway, lets say 45mph or faster and i slightly hit on the brakes the steering wheel starts shaking out of control. Could it be that the rotors are faulty??

might be. Check the rotors with a dial indicator. Although i might suspect other front end parts

i changed my rotors and the mechanic didnt change the breaks, and like a month after that service when im drivinga on a highway, lets say 45mph or faster and i slightly hit on the brakes the steering wheel starts shaking out of control. Could it be that the rotors are faulty??
Bad "thrust arm" or upper control arm bushings. Plus, you MUST follow proper break-in procedure whenever you install new pads and/or rotors. Could also be bad shocks, tires out-of-round, low tire pressure, etc, but those are all secondary to the thrust arm bushings and proper pad/rotor break-in.

Read these and tell ANYONE you know who drives a car about these articles:

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

http://www.stoptech.com/tech_info/wp_bedincontents.shtml

My E34 had the same problem. I had brand new brakes that were extremely tight and had no vibration except for 55 mph under a light foot. I knew it wasn't the rotors because there was also a very slight shimmy at 55 that got worse with the brakes.

I looked up quite a few threads about it, and the common solution was the upper CABs. Mine were about 50-60k miles old, so it very well could have been that. Sold the car before I fixed it though, so I don't know for sure.