Severe pain in left thigh sometimes calf

Hello Doctor, I'm having a strange leg pain. When I'm sitting on a chair or driving the car I don't feel any pain at all but as soon as I stand up even only after 15 mins, I feel severe pain in my inner left thigh. The pain also goes to calf. It looks like the pain is under the skin because it is tender to touch and itchy sometimes. When I start walking, the pain completely disappears after 2-4 mins like it was never happened. There is no redness, visible veins or swelling in the thigh or calf. However I feel the thigh vein hard and knots when touch. One thing to I have noticed is, it happens if I was sitting on a chair where my thigh was pressed against the chair and then stand-up. No pain on sitting only. Could it be superficial phlebitis or DVT?