Suggest Treatment For Recurring Abdominal Pain

My 11 yr old daughter has had moderate to severe abdominal pain that is mostly on the left side but occasional radiates to to middle. They have done blood work, xrays & an ultrasound but everything looks good...she s had been on bactrim due to chronic UTIs & I ve been told that it s constipation or acid reflux, treated both with no relief from the pain...please tell me what I can do to help her be more comfortable or what else her Dr could be doing to figure out this problem