My son who is 6 get feavers every 2 weeks for the last 4 months. His temp goes up to 105.5. His blood work and all other tests keeps comming back normal. What is this?

Optional Information:
Male , Age: 6

Already Tried:
Basic blood work, abdominal ultra sound, head ct w/dye. Seen many docs. still nothing. Seeing an I.D. doc on MON.