Severe Lower Abdominal Pain Everyday At Noon. What Could It Be?

I have been having pretty severe lower abdominal pain every day for the past 2 weeks. I have an appointment with a GI doc on Tues but I'm not sure if I should go to urgent care beforehand or not. The pain starts around the same time every day (between 1:30-2:30)--it doesn't seem to matter what I eat or when I eat. The pain is in my lower stomach area (the whole area not specifically right or left and definitely central). When the severe cramping/pain subsides, I'm sometimes left with a dull ache on the lower left side--but not always. It will last for 1-3 hrs per episode. Sometimes I will get 3-4 episodes per day. When an episode hits, it pretty much knocks me out. I'm in severe pain--a heating pad is the only thing that remotely helps take the edge off and only sometimes. I'm a 30 yr old very healthy female. I had my annual physical about 1 1/2 ago and all blood work came back normal. Any advice?