Unknown blood infection. Do now. ?!

She got high fever and Er CRP level was 13. We took all the tests and everything is normal. Dr gave antibiotics for 4 days and got discharged dat time er CRP level was 11. One week Dr advised to take medication. After a week Again she got fever. We took er to him, he changed the prescription. After 3 days again she got fever and he told to take other tests, scan n x-ray, everything was normal but CRP level was 23.4 so admitted in hospital and gave antibiotics for 5 days. Aftr dey took CRP test again it is 23. We could see the difference in WBC count but still er CRP level remains same. Doctor advice to take antibiotics for 2 more days. But We are worried so much. We didn't know the cause of infection and we didn't know how to control. Dey are also not sure. Please any help on this. What we should do now.?!!