What causes lower abdominal pain on right side?

Few possibilities.: Appendicitis, beginning of large intestine called cecum inflammation and ascending colon , from infections like amoebiasis, invasive bacterial infections , tb, inflammation frpm crohn's diseas&, ulcerative colitis, autoimmune diseases like behcet's disease , tumours of intestines-small , large , bleeding in the rt. Sided mascles covering pelvic bones, abscess-lymphnode &muscle, testicular tumor.

Appendix: Appendicitis would be high on the list in a male.

Many reasons: It depends on what brings the pain on, what it feels like, where exactly it is located, how long it lasts, what makes it better, and what makes it worse. Only a dr. Can help you figure this out. Possibilities include an ulcer, irritation of the stomach/duodenum (small intestine), gallstones, pinching of nerves that exit the back, spasms of intestine, colon cancer, hernia, or if sudden, appendix.