As far as I am aware BV is an overgrowth of certain bacteria in the vagina, just as a yeast infection is an overgrowth of yeast. The PH is off for the overgrowth to happen. The semen can alter the PH level of the vagina as can a period.
It's possible it has reoccured, it often does. Please go back and get retested to be sure. Yo may have also developed a yeast infection from the antibiotics to treat the BV. Be sure though because it doesn't pay to self treat or guess. I'm coming up on 3 months of pain and itching now that cultures clear and it's miserable. I had BV and used the metrogel but the irritation never went away.