I have a 9 year old little girl, who has been having on and off pain behind her knee for about 6 months now. I have taken her to the doctor for this twice now. Both times xrays were done and came back normal, blood tests were also done and came back normal. She is limping and on pain, at time she is crying. They are sending her to an orthopedic. What could be causing this?? This is so frustrating and confusing when you cant help your children.