What Could Cause A Toddler’s Fever, Sinus Congestion, And Headache For 3 Days?

Hi! I have a 3 year old healthy toddler who’s had a fever, stuffy sinuses and headache on and off for going on 3 days. The fever hasn’t been higher than 101.3 but has mostly oscillated between 99-100.5. When she takes Motrin she’s pretty active but not 100% I plan to call her pediatrician in the morning but I was hoping for some assuring words to get through the night. Any idea what this could be?