What do I do with a 5 month baby who's running a temperature of almost 101?

Fever is > 100.4. Acetaminophen should be given to help with fever control. Ask your pediatrician for the right dosage, it's dependent on your child's weight and age. Your baby should be taken in to see his/her pediatrician asap, to rule out an infectious process. Most fevers are caused by viral infections, but infants less than 6 months of age with fever need to see their doctor!