You have had a very rough course from your prior spine surgeries and the attempted fusion you underwent unfortunately had a low rate of success. Without mechanical stabilization of the vertebra (rods and screws or an immobilization brace), fusion rates are very low (maybe in the 50% range).
You have lower back pain and sciatica. What is the percentage of both together? Do you have more back pain than leg pain (70/30, 60/40) or the reverse?
The disc prolapse at L5-S1 can possibly be surgically treated and your lower back pain can also respond to surgery. You need to find an experienced and thoughtful spine surgeon to perform a complete work up.
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.