I need to loose at least 50lbs, im 21, 5'3" and 212lbs, but every exercise I do hurts, esp my lower back and bad shoulder. Any advice please?

Start Slowly. First, rome wasn't built in a day and neither is your body. Start with gentle walking. Just go slowly at first and everyday do a little more. Your goal is to walk everyday. After some time your body will adapt and you will be able to do more. Then you can focus on getting your pulse up for a sustained time. During this time, take notice of how you eat and why you eat. Good luck!