The pain caused by the kidney is typically felt in the flank area, which is on the back just at the lower edge of the ribs on the either side of the spine. This pain is sharp, severe and occurs in waves. Similarly, back pain, which is usually dull, may be equated to the kidney pain but it's caused by muscles, ligaments, or vertebrae and disks of the spinal column. Kidney pain is most commonly caused by kidney stones or infections. It seems that the cause for your pain (if the above mentioned problems are excluded) might be repeated infections of the urinary system. Urinary infections can occur often, especially in the women. The rash on the skin like the one you describe may appear if there is kidney failure, which is not the case here, so I don't see a direct link between your kidney disease and the rash. Nonetheless, you can follow up with an internist or nephrologist (kidney specialist) for further advice. You might also want to consult a dermatologist about the skin rash that has appeared on the legs.