Most generally but not always, clear, white or light yellow mucus despite the amount or thickness, does not mean infection. There are some exceptions though. Do you have pressure in the sinus area? Allergies alone can cause excessive secretions. The only way is for a doctor to either culture your nose or thunk on your sinus cavities lightly with their fingers (not sure what they determine from this but this is what mine does to me).

Z-Pak is in the "mycin" family of antibiotics. Chances are that if you are allergic to that, you will be allergic to anything in that family. I am not personally familiar with Avalox, so not sure what family it belongs to but you might ask either your doctor or pharmacist about it. Can you take penicillin? I have found Cephalexin and Amoxicillin (both pencillin off shoots) to be effective.

Good luck.