I sprained my left calf muscle 14 weeks ago. by the end of the night, it is tight and a little swollen compared to the right one. i had an ultrasound done a month ago and no clots were present. what is causing this?

Different things: you sprained your ankle 14 weeks ago. That refers to the ankle joint not the calf muscle. You had an ultrasound to lookfor blood clots in the vein, not muscle. All of this is good information. Talk to your doctor about your concerns. Do you still have pain, limits in range of motion. Is there a knot in your calf? These are the next steps.