I have severe pain on upper calf and knee when i stand and walk. there is no swelling or heat and i have not injured my leg - what could the cause be?

Calf pain : One sided severe calf pain and referred knee pain in the absence of an injury present while walking suggests presence an intermittent claudication from arterial insufficiency i.e. Plaque, clot, pad). Unexplained calf pain presenting in this fashion may also be do deep vein thrombosis (venous clot), but less likely to subside at rest. Both can be very serious and should be evaluated.