This is Dr. David
I am sorry you are having such bad vertigo still.
the zpack should be able to kill any bacteria in the fluid in the middle ear.
you should also try antihistamine allergy medications like Allegra, and benadryl at night time which can help dry up secretions and sinuses and help fluid drain out of your inner ear
to open up your eustachian tube which drains out fluid out of the inner ear, try to yawn and thrust your low jaw forward at the same time to open up your eustachian tube. this might help drain fluid out of your inner ear and help decrease the vertigo.
make sure you take the steroid pills first thing in the morning with food in your stomach. don't stop your steroids suddenly, you want to taper them down slowly.
you can also try dramamine over the counter dizziness medication.
if after all of this you are still having dizziness and vertigo, go back to the ER and ask for scopolamine patch to help and ask to see an ENT doctor in the ER
let me know if you have other questions.