See a Doctor! When you have pain your body is trying to tell you something.

fwiw, I messed up my knee and needed surgery. At the initial rehab eval. the PT went nuts! My right hamstring was just a mess, a tight contracted mess that wouldn't relax. I also had lots of lower back pain. A couple of weeks stretching out the ham string and the back pain is mostly gone.

I do get serious lower back pain after sailing the F16, I think it's from sitting on the hard hull. Stretching relieves that pain. However, when I sail a Weta, sitting on the tramp with my knees bent in a normal sitting position, no pain. Jus' sayin'...