Welcome to the forum.
Brownish red spots on oral mucosa
could be signs of a viral infection or a significant bactetial infection causing petechial rash
i.e small spots caused by bleeding of minute blood vessels or capillaries.
As currently he is not under any antibiotic therapy, I would suggest you consult his pediatrician
for a thorough examination and if required few tests like the complete blood picture, throat swabs etc to confirm the diagnosis.The treatment would depend on the diagnosis mostly oral antibiotics
Please do not panic as the present situation is not an emergency, but definitely warrants further investigation and treatment by a doctor.
Till then ,
Give your child plenty of water and other fluids.
Make him do warm saline gargles thrice daily.
Continue the antipyretics like tylenol for fever.
I hope this information has been both informative and helpful for you.
You can consult me again directly through my profile .