It is not the exact same drug but it belongs to roundabouts the same family (the macrolides). Considering that your doctor prescribed you another one from the same family I have a feeling that he thinks it's just a side-effect of the antibiotic that made you sick and that you are not genuinely allergic to this particular family. (Biaxin's some nasty stuff and makes lots of people sick.)

That said, if you're having the same symptoms of feeling super icky (which I suspect have something to do with not being able to keep food down?) then you should still have your antibiotic switched -- another reason why culture and sensitivy tests are super-awesome -- because they then have a lab-approved list of weapons to use in their arsenal.

Biaxin/Erythromycin and Levaquin (levofloxacin, a quinolone) are different drugs that work in different ways and as far as I know kill different things. Levaquin is a big-gun broad spectrum (both gram negative and positive) and Erythromycin is usually saved for S. pneumoniae and S. pyrogenes, and atypical (mycoplasma) pneumonia. They sometimes use it for the H. Flu but lots of them are resistant to Erythromycin so there's better drugs for that.

Erythromycin interacts with quite a few drugs, like the bennies (valium-type drugs) theophylline, digitalis, and the non-sedating allergy drugs terfenadine (Seldane) and astemizole (Hismanal).