If you had a kidney stone, the CT-scan would detect it. Pain that originates from a kidney stone can’t be provoked by simple touch or felt when you lay down. kidney stone pain can be provoked by a hit in the side on the backside of the lower abdomen, so called the "sucusio renalis". According to the description of “pain in my back at the end of my ribs whenever it is touched or I lie down”, you could be experiencing some muscle pain that originates from the muscles on the back. You may consider taking painkillers to temporarily relieve the pain and seek help from a general practitioner for a check-up.