My son suffering with fever. Suffering!

Since March this year my child is suffering with fever 98 -103 , sometimes while teething after the celebration of his first birthday in Feb, recurring 20-25 days once, sometimes 15 days . First  time suffered with fever we had consulted the pediatrician prescribed paracetomel and some antibiotics, but it's lasted for 6 days, done blood normal and culture test, urine normal and culture tests, ultrasound, jaundice , malria typhoid but all showed no infection. It reduced in 6 days. But again fever repeated in April , may, June . But in June it has comewith febrile seizure, doctors used medication for fever ,seizure ,Decreased and discharged . After 15 days again fever happened now without any infection , we the family can't understand the reason since the doctors consulted just said infection. I should mention that my f in law has fits. Now I want to know the reason behind this . During all this my child has been facing severe pain while saline, please  save my child from this suffering