Physical therapy can leave you sore after a work out, but it isn’t supposed to cause pain. If you are experiencing pain with your physical therapy, you should speak to your therapist about where the pain is, what seems to be causing it, and what type of pain it is. This is essential because if your therapist doesn’t know that you are hurting, you could be doing more harm than good.
On the other hand, if you are talking about soreness from using the muscles and stretching, this isn’t unusual. Most people have waited quite a while before going for back surgery. During that time, by adjusting your posture and how you do things, you most likely put as little stress on the affected muscles as you could. As a result, they weakened and now need to be strengthened again.
Again, speak with your physical therapist as any pain or discomfort could mean that you may need to have your exercises changed a bit.