What Causes Severe Leg Pain And Difficulty To Stand?

my daughter has tingling in her feet and can not stand straight as her calves hurt. He can barely walk and when she sits for any amount of time, when trying to stand the pain is worse. She has been on birth control to help with the heavy, painful periods which did help but she is still having the leg pain. I took her back to her gyno today and we are being referred to a spinal specialist. I did ask if this could be endometriosis but her doctor didn't think so as her cramps seemed to get better. She is 16 years old and I hate watching her in such pain. What could be causing this and are we heading in the right direction going to the Spinal Institute?