What Causes Intermittent Lower Abdominal Pain?

My 14 year old has been experiencing infrequent lower abdomen pain (usually starting in the middle of the night and going through mid-morning). This has occurred for the past 2 days. He is now experiencing it in the evening to the point where he bends forward from the pain. He has had a bowel movement today. Is this something I should have checked out at the ER?