Hi lfc runner
have you done any rehab to strengthen the torn hamstring? You need to specifically strengthen a muscle if torn and stretch it as it heals with scar tissue which is inelastic.
Try some prone (on front) hamstring kicks to start with lying on stamach kicking heel to bum slowly then increasing speed.
This can also be done in standing. try some bridging to see if the gluts rae working or are the hamstrings doing all the work shouldn't feel them doing a bridge. If this is the case your hamstrings have been overworking which is the cause of the tear and you need to also work on your core.
You also need to strtech the quads and hip flexors and if these are tight then the knees can be sore.
try the Thomas stretch and see if legs hang to a straight line or are hips tight and knee lifted.
thses exercises should all be on the website if not Alice can you put them up again!
Thanks
Sarah