I have pneumonia and have had fluids pulled off lungs. it keeps coming back. why is this happening?

Pleural effusion: Pleural effusion or fluid around lungs is a common complication of pneumonia, occurs in 30-40% and a lot of time depends on what type of bacteria causing pneumonia. Sometimes when it's not adequately drained first time, it may require repeat drainage or even chest tube or surgery. Other underlying medical problems such as heart conditions or weakened immune system or smoking also prolong recovery