One of the hardest but most effective in reducing hamstring pain is the nordic hamstring exercises. in kneeling with your heels secure you lean forward to get your nose to touch the ground and return - near impossible initially. Took the girls in my year who were doing a study on it 6 months before they could do it. More recently the exercise has been turned into a drop catch - very good for the tendon... hense you drop then catch with your hamstrings - you'll fail everytime, it's pretty much impossible and hense you plant the ground and push yourself back to upright...

words of warning - very hard exercise! and you must get into it graded... your best to have a very good Personal Trainer or a physio guiding you through it - with recurrant hamstring pain you will need to be sure you won't pull your hamstring doing the exercise.

When your pain occurs in both legs then it is very valid to assess ankle knee hip and lumbar spine. ensure you have appropriate footwear.

Perhaps revisit the sports physio and get further assessment and ask them about the nordic hamstring exercise - it's operating on the Mechanotherapy principal by Kham and Scott in Br J Soprts Med 2009 - free to find online for the therapist if they aren't up to date.

Have a good one.