Does Metronidazole affect Yasmin contraceptive pill?

I've been taking it pretty badly and not really stuck to the course, but it's not for a big infection and the infection appears to have gone away. Anyway, I'm concerned that it will have affected my pills? However, I have heard that vomiting and having diorhea can increase the risk of getting pregnant if you don't use other protection, so surely the risk is higher than that? Also, several times, I have had unprotected whilst on the pill, and not once has it gone wrong. What should I do? Thank you x