Low grade fever
and rhinosinusitis could be a viral infection making your allergies worse. So depending on which part of the world you live in, appropriate blood tests will be required.
If however, this is always the case skin prick or specific IgE blood tests is important to delineate your allergies.
Antihistamines, nasal sprays and inhalers for the lung is otimal medical control that must be part of the management plan.
Pulmonary function tests is required to ensure you do not have asthma
if not already diagnosed.