Just walking stopped and turned and felt a pop on inside of left knee, and now in knee pit area is sore it's be about 4 days, little more sore each da?

Popliteal cyst.: This may represent a popliteal cyst, otherwise known as a Baker's cyst. The movement you describe represents a torque upon the knee, wherein you turn your body upon a planted foot. The knee does not like torque - it leads to pressure buildup within the knee that can lead to a herniation of synovial fluid out the back of the knee, the popliteal cyst. Give it some time.