Fever is due to infection. If the child has no other symptoms except fever , likely it is a systemic infection. Needs further evaluation including dengue, malaria, urine infection, viral fever etc.
The medicine the child has already taken is symptomatic and that's why fever is coming back in absence of symptomatic treatment.
Initial antibiotic is only empirical and to be modified as per further reports.
Next Steps
follow up with your paediatrician at regular interval until the diagnosis is made.