Your history leads me to believe that you might have developed herniated a disc at L4-5 or L5-S1 compressing the nerve root and causing leg pain. A positive EMG report indicates that you probably have motor weakness. Rarely, a positive EMG report may just indicate nerve irritation but most of the time will pick up muscle involvement.
Walking pain as compared to sitting and bending pain may indicate a disc hernation in the “far lateral” or lateral recess position but may also indicate foraminal stenosis from degenerative disc disease (see website).
You need a spine surgeon to examine you and an MRI of the lower back will be necessary.
Dr. Corenman