Sudden onset of unilateral left calf pain (anteromedial part)?

I was awaken from my sleep bec of the pain, though it's tolerable it's so uncomfortable. It dont occur that often but when it does it's so annoying. Im using a thermal blanket to keep me warm, no recent fall/ injury,negative swelling/edema.What could have caused this throbbing/tightening pain? I noticed a little blue vein about half the size of a penny lower half from the knee just right between tibia and the medial gastrocnemius muscle. SHould I be worried??? I need serious answers only. Tnx