Call your doctor right away if you have severe back pain post your workout or any stretching activity. If you have a milder pain, try taking complete rest but then if the pain still persists; please check with your doctor.
Also consult your doctor if you have any of the symptoms relating to back pain. In most cases, you would be okay from getting some rest. You shall also ask the doctor for the specific back exercises which are good for your back and do it regularly to avoid the recurrence of the back pain.