What are the symptoms of worsening pericardial effusion, which was previously small?

Shortness of breath: Why are you having pericardial effusion to start with -- being so young? Was it infection? Or connective tissue disease?

Fatigue, short breat: A pericardial effusion limits the ability of the heart to fill and so to pump blood. There can be chest pain, worse with breathing, shortness of breath and/or fatigue. There may be swelling of the legs (edema).

Dyspnea: Shortness of breath and if that starts to occur, it's indicative of early tamponade and a medical emergency as the next symptom is likely to be low blood pressure (shock) and death. Pericardial effusion per se causes no symptoms. Tamponade causes symptoms. Pericarditis, with or without effusion, can cause chest pain.

Chest Pain: Pericardial effusion can be a problem if not monitored by your cardiologist...Chest pain, shortness of breath can happen. If so, this is a life threatening condition and needs to be treated immediately. Usually, pericardial effusions caused by viruses get better on their own. An enlarging effusion is worrisome and needs to be evaluated asap. Go see your doctor asap.