My left hamstring has been very tight the last few weeks. Yesterday after jogging I was walking downstairs and my leg totally gave out on me. My leg currently is very painful and burning from what feels like the middle of my gluteus, down the back of my leg to my knee, kind of wrapping around the left to the front of my knee,the back of my knee is slightly swollen. I had ACL surgery 6 years ago, never had any trouble with the reconstructed knee. I jog 2x a week, do pilates 1x week, walk every day.