Hi and welcome to HCM.
I dont see why are you giving him antibiotics if he doesnt have uroinfection. But ok. Dilated renal pelvis
isnt uncommon and it usually doesnt cause permanent problems. It is questionable does he have impaired renal function because dilated pelvis doesnt mean taht his renal function is affected. It should be evaluated by measuring urea and creatinine
.If this is normal you can give gripe water. WIsh you good health.