I Injured my Back at work can I get workers comp? And will the company Fire Me for doing this?

You need to file a work comp claim asap, that is the job of the injured worker. Despite what others have said, if you were on the premises you are pretty much covered despite the fact that you were unloading a truck. You cannot be fired for filing a work comp claim, but companies do find other reasons to get rid of an employee with a bad work comp claim. Each state is different in regards to work comp laws, you probably can go to a doctor of you choice, but call your HR to find out. You need to file a claim, the longer you wait, then your adjuster will think you did something else and are trying to get it covered on work comp.