Although it is more of a muscle growth story, there's quite a bit of breast expansion and a lot of lactation in that thing.
Enjoy!
Her Muscle Milk
After the birth of her daughter, Anna is unhappy with her body. Her husband gets her a training handbook, and she starts using it. Soon enough, she starts to like the transformation. Things go crazy when she learns that her milk now has a special effect.
This erotic fiction contains female muscle growth, breast expansion and lactation. All sexually active characters are at least 18 years old.
https://www.smashwords.com/books/view/935111