I would recommend figuring out what could be done to exercise with the current state of your body, and what could be done to rehabilitate your shoulder and focusing on that. If you have PT to do for your shoulder, start with that as your exercise for the day. As your shoulder heals, you can try balancing that out with your other arm, maybe a small 2 lbs dumbbell. As far as your back and leg are concerned , I would say to check with a doctor to make sure there’s nothing else going on, but start with standing up and simple stretching as part of your routine, then build up to a few minutes walk, and enjoy that for a time. My biggest lesson with creating an exercise habit has been to start right where you’re at, and not anything beyond that!