I remember reading a while back that all of your muscles are connected by tendons, ligaments, etc. in a chain from your lower legs, up one side of your body, then down to the other side to the other lower leg (rather than these isolated chunks we are all taught) and even cross over from right to left in several areas. I teach Anatomy/Physiology and I emphasize this to my students - everything is connected! In my case, my weakened hamstring resulted from training a very specific set of muscles to do olympic lifting and ignoring a weaker side. This resulted in strong but very tight muscles down the back of my body, despite having an excellent coach/trainer. One of my poor hamstring muscles was the symptom of that. Something had to give and that was it.
Are you doing all three stretch series? Those have been the most helpful for me along with the mobility exercises in Foundation 1. I can't recommend them enough. I am certainly nowhere close to the mastery in the videos, but I am taking my time and doing as much as I can and the improvement in my hamstrings, back, and shoulders is measurable. I marvel at the flexibility demonstrated in the videos and chuckle every time I hear Coach Sommer talk about Orench's body of stone from weightlifting. But hey, I am much older than you, so you should progress far more quickly than me! I think I will be in F1 for a long time. 
