It is certainly possible that a recent parvovirus infection can cause fatigue and lethargy. It is less likely that it could be EBV since it was a past infection.
Your WBC is low, suggesting a possible immunocompromised state. There are many, many other things that can be tested for including the following:
HIV test
thyroid tests
blood cultures
PPD looking for TB
ANA, ESR and rheumatoid factors looking for any acute rheumatological states
CT scans looking for abscesses or lymphomas
These are all tests that should be considered if there is no clear source of fever. More concerning is the fever in combination with the low WBC count - this should be evaluated by your personal physician or a hematology specialist.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.