It may be premature to embark on PT and exercises to strengthen the shoulder until you have the MRI and a diagnosis of exactly what is causing your frozen shoulder and the location of the problem.
My frozen shoulder was caused by a bone spur, which as it grew, and subsequently damaged surrounding area, literally froze my shoulder. I was unable to raise my arm much past my waist level, and it was so painful that, well I don't even want to remember how much it hurt. After several months of PT, I finally got the MRI and at that point we realized that all the PT in the world was not going to help until I got that bone spur removed. By waiting so long to do the surgery, the recovery was prolonged. I only wish now that I had done it sooner. Even still, it was about a year after the surgery before I had regained full range of motion, and that's after months of PT, and continuing to do all the exercises every other day.