Is kidney pain normal during the colonoscoppy prep. been having bad stomach and back pain since yesterday?

No, not normal: I'm not certain what you mean when you say "kidney pain." Usually this means flank pain--side back pain around the mid-back. The usual complications with prepping (usually drinking polyethylene glycol solution) can include nausea, vomiting, cramping and/or abdominal bloating. Rarely electrolyte imbalances such as low calcium or high phosphate can lead to kidney problems. Call you doctor NOW!