Is there a natural supplement equal to metronidazole?

Over a decade ago, I was put under the knife in an intense abdominal operation. After that said operation I developed uncontrollable gas. I was told it was because of "bacteria overgrowth", and was put on flagyl, and that took care of it.

I don't feel too safe relying on an antibiotic my whole life, my gas problem is getting to be really uncomfortable in social situations. Is there any alternative for flagyl that I can purchase OTC?