Hi
Thanks for questioning to health care magic.
As you stated that stones passed and there are no stones in both kidneys.
Still symptoms persists .
Urgency , frequency and burning micturition .
May be due to these possibilities , these include;
1 Concretions ( very small in nature ) .
2
Urinary tract infection , diagnosis can be confirmed by examination of urine in a lab.
3
Anxiety , as I have seen so many patients who passed stones and still remain in trauma of stone for some days .
Your son might be in trauma phase , so need not to worry .
Plenty of fluid intake will help .
Hope this information will be helpful for you.
Good luck for your son.