Internal Medicine doctors would rather tell a mom not to breastfeed than actually take the time to investigate whether the medication is safe to take. I stopped nursing my son when I had to go on long-term antibiotics, and when I told this to my new OB during my second pregnancy, he said that I could have continued breastfeeding on that medication and that I should always check with an OB or pediatrician to see if medications are safe during breastfeeding.
You can take hydrocodone (vicodin) while breastfeeding. They prescribe it for moms after c-sections all the time. I would definitely call your OB or pediatrician about the antibiotic. I just finished giving amoxicillin to my 4 month old for an her ear infection. So it's probably safe for you to take.