This sounds like Manikins, by John Varley.

"No, no." She laughed, without humor. "There's no such thing as a man, the way you're thinking about it. Only women who've been taken over at birth by these, these..." she groped in the air for a word hideous enough to express her distaste. She couldn't find it. "Things. Organisms. I said they invaded the Earth, but I'm not sure. They might be from here. There's no way to know, they've taken over too completely."

-https://www.facebook.com/notes/sol-aris/manikins-by-john-varley-1976/10151440227880688/

This is Manikins, by John Varley, according to the OP.

"No, no." She laughed, without humor. "There's no such thing as a man, the way you're thinking about it. Only women who've been taken over at birth by these, these..." she groped in the air for a word hideous enough to express her distaste. She couldn't find it. "Things. Organisms. I said they invaded the Earth, but I'm not sure. They might be from here. There's no way to know, they've taken over too completely."

-https://www.facebook.com/notes/sol-aris/manikins-by-john-varley-1976/10151440227880688/