There may be many varied reasons for low back pain.. The cause for the same should be ruled out with the help of x ray or MRI depending on the severity of pain..
Next Steps
He can start hot fomentation, take analgesic with muscle relaxant tablet, apply analgesic ointment locally..
Health Tips
Avoid heavy work, avoid sitting down, avoid Indian toilet, avoid forward bending..
Regarding your query for Medical certificate, it is not an option in online consultation..