Thank you for your query on Healthcare Magic.
I advise you to give meftal if there is high grade fever like more than 102 degree F.
Below that temperature simple paracetamol
syrup is enough in prescribed dosage.
If there is high grade fever, you can do tepid sponging with lukewarm water after giving an antipyretic
The weakness is due to high fever
and may be due to decreased hydration status as he is taking less orally.
Try to maintain his hydration by giving sips of oral rehydration fluids like Pedialyte
Consult your Pediatrician
again for re evaluation and for investigations if required.
Hope I have answered your query.