Hi welcome to Health care magic forum, If the symptoms are not alarming you can consider it to be starting stage of the disease. If the symptoms like pain and breath less ness is more you can conside it is in advanced stage,
pleural effusion is of 2 types, transudative with clear fluid, and exudative, some what severe disease. it is caused by c.c.f.(heart problem),
pneumonia, t.b,
liver disease,
renal disease, auto immune disease, etc.
It is diagnised by x.ray, c.t.scan,
ultra sound scaning. Fluid is removed by Thoracocentysis, ortube thoracectomy.
Pleurodesis, pleural drain or pleural decartication are the other treatment measures available in advanced cases , of course not in your case.
The removed fluid is to be examined in the laboratory for actual diagnosis. and treated accordingly, for complete cure.
So i advise you to consult a chest physician for diagnosis and complete treatment. Wishing for a complete and fast recovery , and thanks for calling.