I had a disc removed ( L2) pain in my lower back has never improved?

Hi there, just over a year ago i had a disc removed ( L2), I’m fully aware of any side affects which have been slightly improved with physio, pilates and general fitness regime, however, the pain in my lower back – central and left to right has never improved,. I’ve bee back to the GP and had another ultra scan on the initial operation point but nothing found ?? no attempt was made to scan the other areas in pain. I’m not on any type of medication although i do have lots left over, morphiene, co-hydracodiene, napraxin etc. I’m in constant pain and would really appreciate your thoughts on why I’m still suffering with pain !!