What Causes Pain Below Knee When Pressure Is Applied?

A few weeks ago, I had my legs up on the ottoman. My right leg was on top of my left leg. I got a sudden sharp pain, which felt bone deep. It was like my shin/calf area just below my right knee was in a vice. Within seconds after separating my legs, the pain subsided. The pain was more than a normal ache in that it really got my attention and scared me. I have had three other instances over the last few weeks in this spot. It only seems to occur if my leg is pressing against that spot or if I curl my leg underneath me while seated. I do have a desk job and drive two hours each day and probably have not been getting up to stretch my legs often enough. I have no noticeable swelling or discolration. I do have a enlarged looking vein/artery(?) running across my left knee cap and inner knee area. I am 42 year old and probably 10 lbs my ideal weight, but am in otherwise good heatlh. Thanks for any advice you can give