My toddler has hives and a fever?

My 21 month old son developed hives over a week ago. He's been to the doctor and they gave him Atarax and Prednisone. The hives are still there. He's also had a low grade fever (100.4-100.6) off and on, which I've treated with Tylenol. The doctor does not seem concerned at all that he's had these hives for 10 days now, and when I call he just tells me to keep giving my son the medicine until it's all gone. But the medicine doesn't seem to be doing much. The hives have cleared up a little but they are still there. Is there anything else I can do to get rid of the hives?