I would stick with your physio and get them to examine more into the McKenzie stuff. Your crease is just a lateral shifting of the spine, all quite normal, but can be in response to pain stimulus. This can be towards the irritation or away from. Either way point it out to your PT.

All you signs and symptoms are great information for your treating therapist and they rely on them to assess, adjust and progress treatment. Getting rid of the initial cramping symptoms was only the first step. It sounds like it was a good one so it will not go away in 2 or 3 treatments. This will take a solid body of focused & progressive rehabilitation to both give the tissue a chance to heal and to prevent undue stresses on it in the future.