[evansmom]

I am reminded of a young man in my neighbourhood who, for a number of years, had fevers that came and went in cycles. He'd be well for three weeks, then bedridden with fevers, fatigue and headache for one week. This would go on and on. He also could not get a diagnosis. He travelled with his fiance to Mexico for vacation (in my opinion, no one should travel outside their country when they suffer a mysterious undiagnosed illness) and sure enough, he became very ill and was hospitalized down there.
To make a long story a bit shorter, at the time he became acutely ill, his body was riddled with an etremely high number of copies of the EBV which then led to an immune dysregulation disease called hemophagocytic lymphohistiocytosis (HLH).

There are other things to consider as well: Cyclic Neutropenia, or perhaps low IgG, IgA and /or IgM levels.