When I wake up in the middle of the night my back hurts when I take a deep breath, could this be caused by a full bladder?

Yes, possible VUR. Having a full bladder may cause lower back pain. For example, there is a condition called vesicouretral reflux (vur) in which urine "backs up" from the full bladder through the ureters and into the kidneys. It can be diagnosed via ultrasound and other procedures. More information: http://kidney.Niddk.Nih.Gov/kudiseases/pubs/vesicoureteralreflux/#what. Good luck!