You symptoms may be related to gastrointestinal, urologic or musculoskeltal etiologies. The simplest approach would be systematically eliminate items one by one. If you had an ultrasound and are going to get a CAT Scan, GI and GU symptoms should be fairly easy to exclude for the most part (barring some limitations if the study is not done with contrast). A urinalysis would be the quickest and simplest way to see if there are any urologic issues. If you have blood in your urine then the focus of evaluation would be urologic. A completely normal urinalysis, although reassuring would not entirely exclude urologic issues. As far as kidney stones, unless a large stone with shadowing is noted, an ultrasound is not the best test. A CT will delineate stones. The prescence of stones by CT does not mean your pain is caused by. In general a stone that is in the heart of the kidney ie not within the pelvis, ureter or passing would be unlikely to cause you pain. If the stone is in any of the locations noted previously, then yes it could be the cause of your pain. Because you mention lower abdominal pain, other items to consider would be divertiular disease, appendix and visceral organ related issues. Once you have a CT done and a urinalysis, you should be able to exclude or diagnose most common causes of your presenting symptoms. If these are negative, then I would proceed with musckuloskletal pain work up. Please note that the classic presentation of kidney stone pain (renal colic) would be back/flank pain that radiates to the groin or lower abdominal quadrants.