My symmetry is off but only on the lower jaw of my model? I am making a Chimpanzee skull and everything was fine until a few moments ago when I started to work on the lower jaw, I realized that the symmetry was off even though I didn't mess with it. 

Does someone know how I could fix it?
At a glance, it looks like the lower jaw is a separate object (correct?) and that the origin of that object has been accidentally moved somehow. In Object Mode, select the jaw, right click, and go to "Set Origin". You should see a few options; select "Origin to Center of Mass (Surface)". That should get your origin back to the right place and fix the symmetry.