Hi.. The pain and finger movement might not be due to same reason. Your low back pain could be responsible for your ankle and knee pain..whereas B12 defect could be responsible for your finger movements.. Don't worry everything has a solution. I suggest you to correct your diet..increase calcium and B12 rich foods.... And your lower back need to be assessed properly...to rue out the exact reason for your pain...it could be ranging from disc..neural irritation to SI joint dysfunction ... Again nothing to worry everything has a easy solution.. So I recommend you to meet a qualified Physio or a orthopaedic doctor....proceed with treatment and rehab.. For now....you can ice your low back to reduce the pain intensity.... Put a pillow below your knee to receive pain in the back while sleeping... Hope this is helpful for you.... Revert back in case you need any further clarification...on this...