A bone scan is done not only to determine cancers that has spread to bone, but it also help to diagnose following conditions:
1.Help determine the cause or location of unexplained bone pain.
2.Help diagnose broken bones, such as a hip fracture or a stress fracture, not clearly seen on X-ray.
3.Detect damage to the bones caused by infection or other conditions, such as Paget's disease.
So don't worry at this point of time and go ahead with the investigations suggested by your doctor.