My doctor has referred me back to hospital as my discectomy 2 weeks ago appears not to have worked and i have more pain, what could it mean ?

Several possibe : You could be having a radiculitis (nerve inflammation) or if there was no relief at all from the time of surgery, a fragment of disc may have been missed. If you had a short period of relief & then the pain came back, a reherniation may have occurred. There may be another reason for your pain in the first place other than what your surgery was for or there may be an infection. Ask your surgeon.