How Can Vaginal Odor Be Treated?

My wife is pregnant and we have had sex the last three nights. She has showered every other day religiously for months so it isnt that she is dirty. We have no idea why her vagina smells like fish. It didn't used to and she hasn't had any other sexusl partners but me. I also wash regularly. So disease is ruled out. But what is it? and how can we fix it?