I have polycythemia but im suffering from leg pain: can my blood disorder be the cause of my leg pain?

Yes: Polycythemia can caused sluggish blood flow in your blood vessels. This sluggish blood flow can indeed lead to cramping of the muscles as by products of metabolism are not carted away as efficiently and can build up (things like lactic acid) and cause the cramps. Increase fluid intake, massage affected areas gently, and pause or rest during activity may help.