Nocoxib is NSAID which may cause
hyperacidity, ulcer,
kidney damage,
high BP etc as side effects on prolonged use.
Try to avoid it frequently.
During pains of back, anywhere along
vertebral column, is not recommended.
If the displacement of disc has taken place or intervertebral space/s have reduced, it may be painful but since it's not reported radiating to leg/s, it may not be so severe.
It's definitely some pressure in intervertebral area/s due to trauma caused by jerks etc, may be some
traumatic arthritis which is causing pain. It
should have been repaired naturally but that's why my guess is there's slight displacement somewhere which is not being repaired automatically.
Better you have decided to see your doctor who will see clinically, do x-ray etc.otherwise I would have suggested some herbal antiinflammatory and physio.
Hope this info serves you well.