Thank you for your query at DoctorSpring.com
Pericarditis pain can persist for 6 weeks or more. Absence of fluid doesnt mean you cannot have pericarditis. Fluid in pericardial cavity indicates pericardial effusion not pericarditis. Infact after attack of pericardial fluid develops in between the pericardium layers then the pain will reduce because there is no more friction of the layers of the pericardium.
Pericarditis may be due to infection of inflammation secondary to autoimmune reaction to the infection. Infection of the pericardial cavity is a very serious condition and usually the patient is very sick. Pericarditis usually is an inflammation in response to the infection elsewhere like in your case maybe the throat.
Dr Vivek Mahajan