What Causes Numbness In Leg, Pain In Buttocks, Back And Tailbone?

My daughter is 16 years old and 1 year ago had to stop running on the cross country team. She complained about her "butt" hurting her. I didn't believe her at first and thought it would go away, but after half a year of her not running, In the spring we decided to go to the doctor because it still wasn't going away. She suggested she was having trouble with her piriformis muscle and our doctor agreed.He also said her body is going through this pain because her ligaments are growing too fast for my bone since she had such a growth spurt. she have been going to pt but she still feels the same pain. Her right leg will go numb sometimes, or she will get severe pain in her lower buttocks. Her back hurts most of the time and the area around her tailbone. I can't figure out what is wrong.