Dull constant pain no apparent reason had ct blood urine test nothing abnormal , no gallbladder , pain located side/ back are, what can this be?

Many possibilities: Your symptoms are common, but non-specific. Abdominal pain can result from many processes but i will mention a few. A healthy, young female can experience pain in the side and back from gallstones, urinary infection or obstruction, normal menstruation, appendicitis, ectopic pregnancy, kidney stone, trauma, tumor, and many more. The ct and urine tests are a start, but more investigation needed.