Please get the urine test done and review the reports with a pediatrician as soon as possible. It maybe allergic reaction for which treatment is going on.
If it is related to
kidney issue ie - nephrotic syndrome, urine report will tell. In that case, treatement is different and must not be delayed.
Next Steps
take consult with urine routine examination report.
add urine culture to it if burning micturition was present along with fever