Usually simple viral fevers respond well to even Paracetamol.
It is unlikely that this fever is plain viral fever, if it is having such poor response to strong medicines like mental-p or ibugesic.
And it is already 3 days.
This calls for a thorough check up and investigations.
Next Steps
Consult a Pediatrician in person for examination and investigations as needed, do not assume any fever to be ”just viral” unless said so by an expert. Prompt and early diagnosis and treatment can prevent complications
Health Tips
Consult sos for further discussion