I just got an ultrasound done to check for dvt, but I still have this really noticeable dark blue vein on the back of my knee. I have the same vein on the other leg, just not as noticeable. It is very small, about 1 inch, horizontal, not raised, and dark bluish purple. For around 2 months it has been giving a mild aching pain behind the knee, but then just yesterday, which is 5 days after I got the ultrasound, it hurt really badly like a pulled muscle that started in the area of that vein and extended into the calf. I have no outward signs of a clot besides maybe that vein. It hurts to walk on and straighten. Could the ultrasound have missed a clot?