My son got high fever for 3 days but only fever with a little cold everything else is ok what i can do?

Comfort measures: If a kid is just running fever with no other issues you can concentrate on making fluids available (liquids or water filled foods like apple sauce) and providing comfort medications like Acetaminophen if he is grumpy. As long as he is taking fluids well & playful, it may just pass, & a rash may come out as his fever subsides.If he stops drinking i would have him seen.