The colony count in the urine culture report needs to examined. A colony count of more than 100000 CFU/cumm is significant and would warrant treatment. You could probably repeat a urine culture and if positive again, complete a full course of intravenous antibiotics based on the sensitivity pattern of the urine culture report.
Next Steps
In the meantime, ensure proper perineal hygiene. Avoid bathing in bathtub and always clean from front to back after defecation. Ensure good amounts of oral fluids.
Health Tips
Consult your pediatrician for need of a repeat ultrasound/MCU. More than the medication, recurrent urine infections are harmful to the kidneys if untreated.