Have pcos. only chem menses/3 mos. get bv after each cycle. not sex active. why does this happen?

Bacterial Vaginosis: There are studies showing that Gardnerella vaginalis is the primary cause of BV. This is a normal bacteria that lives in the vagina, but too much of it can cause BV. Studies show that a biofilm forms on the surface of the vagina and be the scaffolding onto which more Gardnerella can grow. This can be treated with 3-6 months use of Metronidazole gel 2x a week.

Check cultures: Make sure that this IS actually bv. A simple vaginal culture with high dose antibiotic therapy should cure recurrences. Wear loose undergarments ( cotton) for 2 weeks- this should resolve on it's own, based on culture results.