 [ Symptoms ] during a genital herpes outbreak if the blisters pop can the fluid then cause additional outbreaks in that individual [ Disease ] most helpful answer metronidazole flagyl does not affect your period however if you are taking a birth control pill the antibiotic can affect how well the pill works    meaning if you did not use another form of birth control it would increase the likelihood of getting pregnant home pregnancy tests are sensitive enough to detect pregnancy if you are one week late if that is a possibility just be sure to get a test that says it can detect pregnancy when you are one week late i looked up the side effects and there is no mention of this side effect here is the link that i found <link> i would call my doctor and take a pregnancy test to be sure