Uti in toddler boy

Has anyone’s toddler son gotten a uti. My son woke up this morning grabbing the front of his diaper and whining and then having a complete meltdown as he was peeing. Brought him to the pediatrician who said “it’s very rare for a little boy to get a uti and all little boys grab themselves for no reason at all” she sent us for an abdominal Xray to make sure he’s not constipated even though I told her has regular bowel movements. I’m so frustrated bc I know my son and the grabbing himself is only happening right before he pees which is why I think it’s a uti. Anyone else experience this?