My son age 3 1/2 years old, now, last months

Patient: My son age 3 1/2 years old, now, last months he affected the fever, we check with child specialist. He taken urine test, blood test, but the results are normal. The doctor given some injection, after three days continues take injection the fever quire. Last week my son said that head ache, immediately we check with doctor and he advised to take head scan, but the scan result also normal. Now, my son said some times head pain and today also he incurred fever 100 degree. What problem my son’s body? I am so afraid. Please reply what steps we take?

Doctor: