Have you had a look at the Askling L protocol exercises and the Askling H test? As to whether or not your gluteal muscles are weak and/or not firing I would hope that a physio would assess these. But back to the start - recovery is all about the right diagnosis - are we sure it is a hamstring injury that is causing your problem? Pain behind the knee after sitting would not make me think of a hamstring injury unless there were other features that strongly suggested that diagnosis.