Hi
Persistent fever while on antibiotics could be explained by 2 things, either the germ causing it is not sensitive to the antibiotics or it is not a bacterium causing the problem.Also, an
enlarged heart with small
pericardial effusion could be the cause of the problem.Pericardial effusion could be caused by Viral infections, cancer,
myocardial infarction, uremia, autoimmune diseases, or bacteria infection including
tuberculosis.No matter the cause of effusion, fever, fatigue, muscle aches are always some of the revealing symptoms.Since most other blood test have been negative, i feel your problem could be from your heart.However, a
blood culture should be done.If the result comes with no particular findings, then you see a Cardiologist for investigation.
Hope my answer will help you
Wish you a quick recovery