What Causes Pain And Tenderness In The Lower Left Abdomen?

I developed strong, occasional pains in my lower abdomen last night , mainly on the left side. It was quite intense while in bed last night, and took me several hours to finally get some sleep. I had a regular bowel movement this morning, and the strong pains ceased shortly thereafter. I still have tenderness in that lower abdomen area, andtoms have been reluctant to eat anything other than toast and cottage cheese all day today . I am a healthy 67 year old retired educator who exercises and gets 8 hours of sleep a night. I take omeprazole daily for heartburn symptoms, but the pain I experienced before starting that medication was entirely different, and was localized in my upper abdomen. Do you have any opinion or advice that may help me tonight if I experience the same bedtime pains? Don.