There are lots of organs lying in the pelvis, which can cause you pain. The bowel is a muscular tube which has a continuous wave of contractions from top to bottom (peristalsis). The most common cause of pain is when the muscle in the bowel goes into spasm; while not serious the spasm can be severe and disabling, leading to concern. The bladder can also cause pain but there are usually other symptoms such as going to the toilet frequently or it is painful when passing urine. The ovaries can develop cysts which can cause pain and the uterus can not only lead to painful periods but can also cause pain secondary to problems such as fibroids or pelvic infection. Cancer in this area does not typically start with pain so this is an unlikely cause of pelvic pain.