reccuring fever in child of 3 years with no other symptoms

My 3 year old son has been getting recurring fever from last 5 months.The fever comes with chill rises high upto 103 and lasts almost 7 days.
The fever goes with crocin.He is all fine for about 15-25 days and then again the fever comes.
There are no other symptoms of cold cough or stomach.
Common blood test,urine and stool tests have been done with cultures but show nothing.
He has been also treated of typhoid, malaria,urine infections (no posive tests) but again the fever comes.
please help and advice

[Yanski]

We have the same situation, my 4 months old son has been having fever since he was 1 month and half. He has been in the hospital for 1 month of on and off  fever. All the possible lab test has been done and nothing really points out as to what is probably the reason why he is having it. The WBC is quite high suggesting that he may have an infection but cannot say where it is attacking since all the test shows nothing. So our pedia checked (us) the parents and found out that I have a developing TB disease and it could be the reason for my childs recurring fever. He could have gotten it from me. So then mine and his treatment started and his fever slows in the 3rd week of medication and we were out in the hospital. But then the fever came back after two weeks of being OK and it would last for 6 to 7 days and stops then come back again in the next 2 weeks. Everytime the fever comes back we would bring him to his doctor and do bloodtest but the doctor would just say that its nothing because the blood test are in fact improving a lot compared when he was still in the hospital. So until now we are still at a lost as to why his fever is keep on coming back.