recurring high fever

my 2 yr old son keeps having fevers of 105 and above. No other symptoms. Has had blood test, blood cultures, seen and immunologist and an infectious disease specialist and no one can tell my why except that it is just my son's body. My gut tells me it is more. It has happened 5 times since May. It is scarey and I am afraid. That is a seriously high fever and what if it goes on forever. Does anyone have any ideas or am I just worrying too much Tweet