Have your therapist go into your gym with you and make sure that you're doing appropriate exercises with good technique. A comprehensive functional gym routine could certainly be helpful in alleviating chronic pain symptoms but as a therapist who works out in a gym I've seen far too many people do some really crazy exercises because they just don't know any better.
Try to stick to exercises that work large and multiple muscle groups. For now avoid focusing on isolated muscle strengthening. Your therapist should be able to give you more details that are applicable to you in the gym setting.
Good luck!