Fever 14+ days/ interstitial prominence on chest xray

My son's had a temperature for over 2 weeks now.  During the day it's gone up as high as 103. He has no other symptoms other than just a fever and tiredness.  His urinalysis test didn't show any signs of infection, he had a flu test & strep test done also with negative results.  Nothing hurts...lymph glands or anything.  We had a number of blood tests done and a couple of those showed that he had a high sed rate (78) and his C-Reactive Protein (CRP) was at 2.7.  This indicates some sort inflamation (inflammation)/infection.  His chest x-ray said "PA and lateral views of the chest demonstrate interstitial prominence, likely inflammatory."  I'm not sure what this indicates.  The dr. said that he may have bronchitis but he's got no symptoms of this.  He put him on antibiotics.  After 4 days he's still running a temperature.  

[remar]

It might be time to get a second opinion. Your son has been sick for awhile now and the antibiotics should be working. Did they check him for pheumonia (sp)? Take care. Remar