Morgan's Curse

Over a thousand years ago, Merlin cursed his cheating lover Morgan Le Fay to switch bodies every time she has sex. She's doomed to inhabit either a pregnant female body or a near-powerless male one, forever. She and her succubus servant are determined to end the curse by killing Merlin while he's still a helpless infant. This story is around 26,000 words long.

I've said that I prefer being a woman, and that's certainly my professional preference. As a sorceress whose power stems from fertility magic, it's pretty much the only way I can actually wield any significant fraction of the power I held before being cursed. But when my curse is over, I actually am going to miss having sex as a man. I find it very hard to decide which gender I actually prefer sex in, because they're both awesome.

...

I smirked and ran my finger along her thigh, and then traced a line up to her belly. “I can. I just can't believe you doubt that I got you pregnant.”
Julie gave me a saucy look. “You're really sure of yourself, aren't you Morgan? It's almost like you're...” and she trailed off. I started feeling distant and disconnected first, and the world went out of focus. The world went dark murky for a moment, and then it shifted and slowly came back into focus. I was still looking deep into the eyes of someone I'd just had sex with, but now I was in Julie's body, looking back into Rudy's face.
I stretched my legs, luxuriating in the sensation of being back in a female body now. I finished Julie's sentence for her as, “...yes, it's almost like we're pregnant, except that we are.” I stretched my limbs and yawned, stretching my body experimentally. No hidden pains, no trick joints that I noticed. Next, I flexed my power ever so slightly with a basic vision spell. As expected, Julie was amazingly fertile, and would've probably gotten pregnant (just not as quickly) even without my Curse's intervention. She was the perfect body to ride into my final confrontation with Merlin.