What Causes High Fever Going Low On Taking Advil And High Back Again?

toddler has high fever for week now. went to 2 docs and er. got antibiotics, but er thinks its viral. no other symptoms. fever was getting to 105 between meds, but now we are alternating tylenol/advil as per the er s instructions and giving him the dose per his weight, not the amount on the bottle. he is dipping really low 4/5 hours after the dose of advil (like 96.5) in the ear, and sweating. but he is still having the fever. is that low ok? the temp is in the ear. and he is very healthy otherwise, acting fine, eatting and drinking. it has not quite been 48 hours on the antibiotics.