It's 2:30 a.m. and you're alone in the emergency room.

A 23-year-old patient had a fever of up to 39 °C (100 °F) and a general feeling of illness two days ago. In the first night there was also a short episode with left thoracic pain. The following day (yesterday) all complaints had regressed completely. In the evening, however, he would have had a fever again and then felt chest pain late in the evening. He therefore decided to come to you at 2:30 a.m. to your emergency department.

What is your diagnosis?