Herniated disc at l5-s1 compresses the dural sac,and lumbar canal stenosis at that area,sciatica(left leg)...do i need surgery??

Probably not: There are 4 basic treatments for this problem. Medication, physical therapy, injections, and surgery. The only treatment which has shown long term benefit is physical therapy. The indications for surgery are intractable pain which had not responded to other treatments or progressive neurologic deterioration. Recent research has shown no benefit to surgery when measured 4 years after surgery.

Possibly: Suggest seeing surgeon to discuss your options if you have completed conservative care.