A 28-year-old male presents with severe chest pain and high fever (39°C) for 1.5 days. Two weeks prior, he had nasal congestion and rhinorrhea. Physical exam reveals slightly enlarged cardiac borders and pericardial friction rub. Chest X-ray (CXR) shows small pleural effusion on the left side. Echocardiogram (ECHO) demonstrates normal heart function with small-to-moderate pericardial effusion. The most likely diagnosis is: