What causes pain on right side of lower stomach?

See below: Many things. Symptoms like these can only be adequately diagnosed through a thorough evaluation by your doctor.

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.