Back pain may be from spondylitis
of facets , disc prolapse
, nerve impingement or muscles...some uncommon but not rare causes are infection & tumors.
Back pain with leg pain is usually due to radiating pain
of pressure on nerves.
Don't neglect if there is numbness and tingling or weakness in muscles or bladder bowel dysfunction.
Please get MRI of spine done after baseline X rays and blood Investigations. It costs about 200 USD in India. Once we find out exact cause we can treat the problem in a true way.