Severe pain left side of tail bone area. Hurts worse to have bowl movement, to bend or lift my left leg. Doctors see nothing on MRI. What could it be?

Tailbone. Make sure your MRI imaged the coccyx. Most MRI's image the lumbar area or sacrum, not the coccyx. Xrays sometimes help. Coccydynia from a fall can cause pain that lasts for months. The treatment is almost always non-surgical. A sitting donut may help keep pressure off the coccyx.