Sharp localized pain behind knee/posterior calf that hurts each time i take a step. no warmth or redness. could this be a blood clot?

Calf pain: The symptoms you describe could certainly be consistent with a blood clot, but may also be explained by a ligamentous injury or something known as a baker's cyst. Any of these diagnoses, but especially the blood clot, need to be evaluated in the er asap and can be easily diagnosed using an ultrasound.

Possibly yes. Get --: Yourself checked out by your pcp or go to an er if a blood clot is suspected, so a doppler scan be done to exclude/confirm it. Generally its due to a pulled muscle, sprained ligament, or a rupture of a cyst behind the knee. These are more commonly seen. Good luck ; happy holidays.