What Can Cause Stomach Ache In A Child?

My 6 year daughter keeps complaining a stomach pain on a regular basis. It is fairly generalised and not in one specific area or focused near the appendix. We have managed it so far (asked all the relevant questions about her toilet habits) and she is perfectly fine in herself, however, she has recently worked out that her stomach hurts whenever she goes to the toilet for a poo. I can't find any help about this online but do not want to rush to the doctor for no reason when she seems perfectly healthy. Any advice would be much appreciated.