May be due to kidneystones or uretric stones..gastric causes include esophagitis, gastritis, and peptic ulcer; and early appendicitis may be a colonic cause. Pancreatic causes are mass or pancreatitis, whereas vascular causes are aortic dissection or mesenteric ischemia...get examined by surgeon and get your abdomen and pelvis scan done... Depending upon the reports they will help you Regards