Son 6 has had a fevet since thursday evening of 103-104.2 on antibiotics since friday night not getting any better any advice on when yo call doc agai?

Now: That is a very high fever. I would not expect that high a fever after several days on antibiotics. Your child should be reevaluated right away in my opinion. The ER would be reasonable.

Infection: Has the Dr recommended ibuprofen or tylenol (acetaminophen) for him? Pediatric doses are usually safe and helpful, unless there are unusual problems. Try cooling him in a cool bath, or with damp towels.. Danger if the fever exceeds 105, or if he has a seizure or altered mental status. Consider ER if this occurs, otherwise call your Dr. to update, and ask for specific guidance

Viral likely: Likely that he has a viral illness. Have been seeing a lot of viral infections that last 5-7 days. High fever the first couple of days then temp down & a bit better each day. Might have sores in the mouth or on the hands, feet or other places on the body. If looks super-sick to you, head to St Louis Children's or Cardinal Glennon to make sure they aren't dehydrated and don't have anything worse.