What antibiotics will cause Birth Control Pills to not be effective?

I was told the antibiotics I am on (Z-Pak) will cause Birth Control pills not to be effective. This was not by my doctor though. I would think since he knows me better and what I'm currently taking etc, would not prescribe me an antibiotic to cause my b-control pills to not work. Is this so? I haven't been able to get pregnant on the pill or had my period on the pill. I have been tested for pregnancy and results came back negative. This was done by blood work. My doctor said sometimes women don't get their period on the pill. Yet, now I am all paranoid hearing some prescription meds cause it to not work?????