the middle spine is the hardest to rehab. You should drop your weight a bit for a few reasons. 1: If you did actually hurt the spine, holding your breath and pushing out a maximum effort will change the pressure of the spinal fluid and that might not be a good thing for you. Do an 80% instead of a 100%. 2: avoid exercise past shoulder level. this will help you exercise with good posture, will minimize compromising positions for a true shoulder injury, impingement, or awkward position while you are recovering. 3: avoid the curled up fetal position while you are not healed. when able, choose a position of extension: which is basically "extension" or for example: if you were on your stomach, being up on your elbows like a child watching tv would be optimal for rehabbing yourself.
Weakness of the arm is concerning. Do you think you hurt your back and its causing the arm weakness or did you also do something to your arm which would directly be causing the issue? If its the back, extension and the prone on elbows should be a daily position of choice for you. If its an arm injury, limit the above shoulder exercises.
Either way it sounds like there's some swelling, inflammation..a new injury. If you are able to ice, do it for atleast 20 min to allow the cold to get deep enough to help. If you have a desk job, roll up a sweatshirt and tie around your waist, basically making a lumbar support..the feel of the material will prompt you to sit upright and this will help a lot. or you can put a facecloth in a fannypack and snap it to your chair..figure that one out and it will help greatly.
