Antibiotics often belong to the same chemical "family" so an allergy to one might very well indicate an allergy in another antibiotic, which you may have never even taken before.

As Karla mentioned, sometimes antibiotics not in the same classification will trigger reactions even the first time. I found this out the hard way.

Once, prior to surgery, I was given an injection of Levaquin (levofloxacin) and was assured by the doctor that I shouldn't have a reaction to it, based on my allergy history. Wrong!

Hang in there and please carry some sort of list of potential allergens with you in case of an emergency.