My 4month old is running a fever no runny nose gave her tylenol (acetaminophen) but fever is at 99.5 was at 100 what do i do next?

Fever: At this early age (less than 6 months old) it is important to have the child evaluated by a physician when a high fever occurs. A fever is typically defined as greater than 100.5, a high fever typically would exceed 102. At this age when her activity and feeding levels are not normal or excessive crying is noted, she should undergo a fever work-up to exclude pneumonia, ear, or urine infection etc.