The only muscle which crosses the hip and the knee and can also give rise to back pain
is the hamstrings. With the history that you have given it will be appropriate that you meet up an orthopaedic surgeon
to rule out any occult fractures
which can also happen in such an injury
. The most probable cause in your case appears to be a hamstring strain which can be treated with sufficient rest, analgesics, muscle relaxants and local balm applications with heat.