What Causes Calf Pain With Tenderness And Tightness?

I'm a 26 year old male, about 5' 9" and 160 pounds, with no serious pre-existing medical conditions to speak of. About three days ago I woke up with pain in my right calf, although only when walking and pushing off the balls of my feet (going down stairs was particularly tough). Since then the pain has subsided significantly, although the interior side of my calf is still somewhat tender if I massage it. There is, however, a persistent tightness in my lower leg, from my ankle to below my knee. I'm concerned I might be experiencing a blood clot or some other more serious condition (though I've experienced no swelling, redness, or discoloration in the limb) as I really did nothing physical , that I can recall, to aggravate my calf.