What Is The Treatment For High Fever , Headache And Body Pain?

my 4 year old son has had a high fever for 5 days, he has bloody mucus and headaches and stomach ache. This was all after he came in contact with a lot of cat dander at a friends house. I took him to the doctor yesterday and she gave him a shot with anitboitics as well as a prescription for anitbiotics. He still ran a fever last night and this morning. Nothing has changed. Again, my son is 4 years old and weighs about 35pds and has no serious illnesses.