I'm happy that you have asked me to assist you with your child and hope that you can benefit from my many years of helping parents like you. Can you tell me which blood tests they did?
It could certainly be a virus but with a temp to 103 for a week it might be worth someone taking another look at him. If you have a children's hospital close by then that would be your best bet on a weekend as a pediatrician will be looking at him and they have all the lab and xray equipment at hand to do any further testing necessary.
Please let me know if you have further questions and if not I would appreciate it if you would "accept" my answer. You may still return with further questions on this topic at no additional charge.