Make sure you are pushing from your heels when you do Smith Machine. In my experience with squats on Smith Machines I seem to push forward, but I finally learned that you want to kinda lean back and push from your heels. Look up at the celing and find a spot, and act like you are pushing toward...
Go to the gym but just don't do legs. Do another body part. Try doing the body part that seems to lag behind the other one. If you are sore, I don't think its good to continue to workout sore body parts.
~lilprincess