Here are a few of my stories that should match your tastes:
Desires
I'm going to put it simple: I always wanted a cock. Since I can't have one, I'll go for the second best thing. Let's see how big I can get by roiding up and building up my muscles. Follow me on an insane trip of muscle passion!
https://www.smashwords.com/books/view/928538There's even an audio version of this here:
https://www.audible.de/pd/Desires-Hoerbuch/B0C6NRK56F?action_code=ASSGB149080119000H&share_location=pdpThe Potions
Jill buys two "magic" potions that are meant to make people sexier from a fortune teller. When her husband tries one of them, he finds that it works. Jill wants to keep up. That's when things go wrong.
https://www.smashwords.com/books/view/724152The Gift of Hermes
Anastasia's husband sends her his newest acquisition: A statue of the god Hermes. Then something goes, well not exactly wrong, and she is changed. She'll need new clothes and pants are going to be rather tight.
https://www.smashwords.com/books/view/768005The Extremists
From the outside, Ayesha and Malik lead a traditional, modest marriage. However, Ayesha is a serious muscle freak and keeps building her body bigger. One day, she suggests getting a second wife for him. But is she only for him?
https://www.smashwords.com/books/view/785436Fury
Bettina and Sibylle find out that they've been cheated on by the same asshole. They decide to take brutal revenge. To do this, they have to get in shape first. Their desire for strength soon becomes addictive!
https://www.smashwords.com/books/view/916587Gym Encounter
One day, Mark catches a look of Denise as she is working out. She is amazing! Fit, sexy, outgoing. He is in love and so is she. However, there is one thing that is keeping her from opening up ... Will he accept her despite her penis?
https://www.smashwords.com/books/view/887176Get In Shape!
After summer break, Nadia is waiting for her friend Alisha who is just as fat and out of shape as her. However, when she turns up, she is completely transformed. Things escalate quickly as Nadia discovers a secret side-effect of the drug she uses.
https://www.smashwords.com/books/view/988113Getting Big
Paula is disappointed with her love life. Somehow, she decides she wants to be as big as her hubby. Everywhere. Thankfully, gene therapy is an option and so, she goes all the way, getting big!
https://www.smashwords.com/books/view/885352Discovery
My wife checked my search history and she found out what I like ... This is very embarrassing, but happily, she's also curious about it. Let's see how it goes ... (Spoiler alert: It'll be great!)
https://www.smashwords.com/books/view/1011678