Hi.
Thanks for an elucidate history.
The child is 9 years old, pain and loose motions, not responding to change in diet.
The most probable causes are :
Appendicitis, lymph node enlargement ( tummy tonsils), meckel's
diverticulitis, and so on.
A proper history, clinical examination, investigations as per these findings alone can lead to a proper diagnosis . This is most important to lead to a proper management/ treatment.
Blood- complete blood picture,
kidney functions tests, blood sugar fasting and post-lunch,
Urine- routine,microscopy, culture and sensitivity ( before start of antibiotic)
Ultrasonography of abdomen.