I had exactly the same symptoms but on my right side. After all the scans the hospital consultant put it down to a muscular/skeletal problem.
Four years on and after a physio assessment I am doing pilates exercises to straighten my back muscles. All part of the aging process but the exercises are definitely having an effect, although the pain is still there it’s not so severe and debilitating as it once was.
I have realised that as I age exercise is a very important part of my daily/weekly routine.