Can mild arthritis of the lower back cause significant sciatica pain? Mri done in july. Pain is getting worse. On gabapentin and meloxicam. Thanks!

Pinched Nerve. Sounds like you have a pinched nerve in your back. I would suggest seeing a pain/spine specialist to evaluate you further to evaluate what level and what can be done to treat you. There are interventional treatments besides medications and surgeries that might reduce or eliminate the pain altogether.
Depends on MRI. It depends on what the findings on MRI where. Usually arthritis (or hypertrophy of the facet joints) can cause back pain that could radiate to the buttocks. 'sciatica pain' usually is caused by inflammation of the spinal canal that causes pressure on the nerve that forms the sciatic nerve. Medications should be accompanied by physical therapy for conservative treatment of this pain.