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Not a slight on jack at all, but statements like that set off my bullshido radar. That would put me off that right away.
What do you do in the gym? Lightish (i.e. not muscle gain) weights for legs and core, stretches etc. This should also be a reasonably factor, time wise, in your running programme. Lots of self massage, foam roller fun, or paid for massage if you can afford it.
Do you squat at all?
Do you squat at all? - Never!
Sounds to me link tightness of hips, and nervous system around glutes and lower back.A lot of the above is correct too. Have a go at this stretch though. Sit on a bench/table having the table edge right behind your 2 knees.Slouch or drop your shoulders/chest towards your stomach exagerating a forward curve on your back.Let your arms hang down to the side.Now try to straighten your leg straight out in front of you.One at a time (OUCH!!)You should feel the stretch from the back your knee to your hip all along the hamstring. Do that nightly.IK (not a doctor/physio)