Has any Girl ever heard of this? BC question?

Ok, I had my wisdom teeth surgically removed last week. They gave me Penicillin to take for 10 days. I took the last one yesterday morning. I'm also on Yasmin. I talked to an advice nurse from Kaiser before the surgery and she said to use a back up method while i'm taking Penicillin and to still keep taking my pill on schedule everyday. I guess Penicillin is an antibiotic that cancels out the birth control so it doesn't work. So since I took the last Penicillin yesterday I called Kaiser again to see how long I need to wait until I can have unprotected again and the nurse said that they are finding out that Penicillin does NOT cancel out your birth control. I guess this is new. She said that I could have had last week and not gotten pregnant. Is this true? She said that the pharmacy and even other MD's will warn you about BC and Penicillin. I'm just wondering why the first nurse I spoke to didn't mention this? Does the second nurse know what she is talking about? Just curious if any other girl has taken Penicillin and birth control at the same time and was still protected by the birth control?