According to the location of the pain (below the knee and to the outside of the leg), you might be experiencing peroneal neuropathy affecting the peroneal nerve or certain of its branches.
The peroneal nerve starts from the tibial nerve. Peroneal neuropathy might be caused by bed rest of long duration, prolonged crossed legs, and peripheral neuropathy.
You might want to visit a neurologist for a physical examination as well as methods for examining the function of the nerve. Meanwhile, avoiding crossing legs might help. If surgery is needed, peroneal nerve decompression might be recommended in which the fascia surrounding the nerves to the lateral side is released thus reducing the pressure which was put on the nerve.