You might not be doing the right exercises, or may have something organic in your back. Its difficult to advise you without any objective data or evaluation. I think you should see an orthopaedic specialist and hopefully a physical therapist, who can teach you some back exercises. If the physician, after examination, feels that you need further evaluation, he may get some investigations like x-rays, MRI, etc done. You should not take steroids for this problem, and at your age with proper diet, I don't think you need calcium.