Immediately call the police and request an ambulance. They will send someone to your location, so stay at the accident scene. Do not leave for any reason, even if the driver who struck you flees the scene. You are required to report an accident if you or someone else suffered an injury, or if there has been damaged property as a result of the accident.
When the first responders arrive, one of the first things that you should do is get medical help. Regardless of whether your injuries are severe or not, it only helps your claim if you get treated right away. Truck accident injuries are usually severe, and in many cases the extent of the injuries demand immediate medical attention.