Kindly advise the treatment for my daughter's stomach pain.

Hi doctor,

My daughter is 11 years old. She weighs 94 pounds. She is healthy but has been experiencing stomach pains for about two months after eating or at random times. She visited her pediatrician a couple of occasions and an urgent care nurse, who have checked her out and done a urine test. She tried Mylanta and Tums, but those have not helped. She feels some pain in the lower abdomen or mid-abdomen, switching around on different days and times. It can happen at any random time and wakes her up at night occasionally. She has her periods these days, but her specific stomach pains do not seem to be just that or come at only those times.