Taking medicine for Bacterial Vaginitis? Don't know what to expect?

[Alutiiq Beauty]

I have been on a flagyl cream for 3 days out of a 5 day perscription. I now have a yeast infection. When do I start treatment for this yeast infection? On day 5, after flagyl treatment? Not ever had this problem, but doctor told me I am alright because healthy woman get this Vaginisis, and not to worry. I would like to know how common this BV is also. As I have my annual exams and have always been fine. My husband and I are trying for another baby, will this affect our chances. Thank You.