Hi..Can understand your concern.As per your query about cause of pain in back and left leg can be probably due to neurological problem like compression or entrapment of any nerve.There may some injury can also cause pain but probability of neurological disorder is more.To confirm this you need investigation like x ray and MRI to be done and a neurologist should be consulted.Till then if pain is more you can take analgesic like aceclo MR twice a day with multi vitamin neurobion forte once a day for few months.Regular exercises or physiotherapy will be helpful.I hope the information helps you.Take care.