acute abdominal pain every 24 hours

For past three days my 9 years old daughter has been having acute abdominal pain, just around the belly button area. This pain lasts only 3 to 4 hours and occurs like clock work every 24 hours. That is to say that it starts around 5pm and ends around 9pm. Over the weekend we took her to the ER they did bloodwork, xrays and cat scan. It all came negative and they don't know what it is, except a suspision that there may be a couple of cysts in her ovary. They gave her tylenol with codeine...that doesn't help much.

We are going nuts, it's been three days and she has this unbearable pain every 24 hours for 3 to 4 hours...Any ideas???

[CalGal]

Have her bowel movements changed in color, shape, consistency? Did the blood tests include looking at liver and pancreatic enzyme levels? Is there any history of GI issues in your family? Any history of food intolerance or celiac disease?