Over use of antibiotics causing BV in pregnancy?

Im pregnant and this is the second time I've had BV this pregnancy. Right now I'm being treated for it with Flagyl as well as using monistat for a yeast infection . what my doc told me...i'm just wondering is BV (bacterial vaginosis) also a result of the overuse of antibiotics? What caused it? I haven't had since the last time i was treated.