What Causes Sore And Swollen Calf?

Hi last night my calf was sore & when l checked it was swollen. At first l thought l d been bitten by something but then realised it was a vein. I walked around & exercised as l was worried it was a blood clot & it went down after a few hours but is still tender & discoloured under the skin. I drove for 6 1/2 hours yesterday but with breaks after 3 hours but have never had anything like this before so feeling a little worried that it is a blood clot?? Will it go away on it s own or should l see a doctor?