4yo is on day 5 of fever 102 & cough. Neg strep. Alternating Motrin & Tylenol (acetaminophen) acts normal when fever is down but lethargic when up. Now tummy hurts.?

Check other infectns. 5 days of fever is worrisome and a thorough investigation is warranted. Many possible explanations are likely, most commonly, other infections (urinary tract?, pneumonia?, kawasaki?, etc). Your doctor should be able to determine.
Mgt. The fever and lethargy associated with your child's cough needs further evaluation. Your PCP will most likely order testing to determine the cause. She may have strep throat, pneumonia, OM, or a UTI for example. Some respiratory illnesses are associated with prolonged fever.