I would go to ibreastfeeding.com and download or purchase the 2006 Medication and Mother's Milk by Dr. Hale. He is the know-all guru of breastfeeding and this book is simply the last word on what you can and cannot take while nursing, how long you need to wait, etc...
What I discovered in breastfeeding 2 kids 2yrs each is that doctors and pharmaceutical companies don't know jack about nursing. They are not taught this in school and no one seems to care to actually research, so they just tell you "You can't nurse." I am not sure about your specific antibiotics, but I know I took standard a.b.'s several times while nursing. SEVERAL times I was also told not to nurse, only to find out it was just fine.
So! Don't give up! Get the book or download it to your computer and read WELL RESEARCHED, SCIENTIFIC data about medications in your milk. It makes me sad when I hear stories like yours, because 9times out of 10, you actually can nurse when you are taking meds. You may have to time your nursing, but it is doable, MOST OF THE TIME.
You are doing the best thing you possibly can by nursing your baby and I admire you for trying to get through this!