I Have Had Pain In My Right Calf, Below The

I have had pain in my right calf, below the back of my knee. It has been there for a while but has got worse. i've done nothing to pull a muscle or hurt it in any way at all. It feels so tight and feels like I can't straighten my leg properly. It hurts to walk. even when I sit or lie down the pain is there. It has got worse, yesterday it was very painful and hard to walk, this morning it feels slightly better but pain is still there. I have read things about DVT and am worried that it could be this.