Blood clots in the vessels of the leg can cause pain, but usually the pain is associated with standing for long periods of time . There may be other reasons for poor circulation as the underlying cause such vericose veins, etc. or there may be a muscle malady.
The poor circulation can occur while sitting for long periods of time. Relief should happen when walking periodically to help circulation.
Hope this helps, and if you have any further questions or comments you are welcome to respond. Take care,