Every time i move my arm, my chest hurts. why does this happen?

Shoulder injury.: The muscles of the upper arm are joined with the muscles of the chest at a complex of muscles, tendons, and ligaments known as the rotator cuff (what we commonly call the 'shoulder'). You most likely have an injury of involving this structure and should see your doctor to determine if any further tests are needed. A mild rotator cuff strain will self-resolve with tylenol (acetaminophen) and gentle stretching.

A few possibilities: This could be muscular or from a one of the joints that joins the upper extremity to the trunk (sternoclavicular) alternatively, it could result from something within the chest wall or chest cavity. If it continues see your primary care doctor.