To continue from the other question you answered,

Given a presumptive diagnosis of influenza and a positive flu swab you initiated oseltamivir 75 mg PO bid x 5 days. She slowly improves over the next 5 days but then relapses and returns with a fever, fatigue, cough and mild dyspnea a little over a week following the last appointment. She is not aching nor does she have other complaints. What is your differential diagnoses now and your next diagnostic steps? ( i think perhaps we may be looking at pneumonia...)