your pain sounds like neurological pain. the indent that you have noticed could be because of muscle wasting in your buttock area as these muscles are innevated by the l5 nerve root. I would be interested to know if you have had an MRI
San and what the results showed I.e. did you have any nerve root compression
as this would explain yor symptoms and the treatment that you have already had. if the injection was around the l4/5 nerve root and it had made no difference to your symptoms maybe you should have a discussion regarding operative intervention.