can happened quite often and occasionally cause the fluid to become loculated like fluid in a sac. So long as the fluid is sterile (not infected) it will dry up by itself but may leave behind a scar which could persist forever. If the fluid is infected or turned into pus, you need prolonged course of antibiotics and the fluid need to be taken off with appropriate procedures either like a drain with a tube or a small surgery ( called decortication or video assisted thoracoscopy
Important step now is to determine if you have fluid in your pleura or just a shadow. You either need an ultrasound
or a CT scan
with contrast to check this. If fluid is confirmed, it needs to be aspirated with a small needle to check the status of the fluid/pus.
Either way, you need further evaluation by a pulmonologist as soon as possible.