My 5 Year Old Daughter Has Had A High Fever

My 5 year old daughter has had a high fever for 6 days. She tested negative for strep and the flu. Yesterday she spiked up to 104.2 temp any suggestions what could be causing this? she had pneumonia about a month ago. And her dr. would like her to get another chest xray at childrens hospital (however, she did not hear the crackling sound this time)