What causes BV after having c-section or childbirth in general?

I do not have BV that I know of,but I have been prone to them since my son was born on July 14,2017.

My obgyn doctor gives me antibiotics for it,but really haven't said what is causing them.

I have heard scent soaps, laundry detergents causes them,but I'm not 100 percent sure.

I also have overactive bladder and interstitial Cystitis if those causes BV.

It's been a battle trying to treat BV every since I got them,and now I have developed PCOS that my doctor has put me on the keto diet instead of medication. Its natural medicine he said. His wife had PCOS and did the keto diet, and now they have two kids. The keto is supposed to help with weight plus helps with your periods also.