I've had pain on the left side in the middle of my back. It hurts more when I breathe in deeply and it has been going on for about five months now. I've been seeing a physiotherapist for three months and the pain seems to be getting worse.
I would speak to the people that are treating you and ask where they stand and how they feel treatment is going. If you feel there is a need for concern, maybe you need to get a second opinion, possibly something may be overlooked.