Could also be Katie's surgery can't remember by who or Erica's belly by theloverofstrangethings who no longer writes.

My mind want to point me at a third but i can't recall its' name right now

(April 30, 2019, 5:24 pm)bigblackman1994 There was a story I had read a few years ago about a woman who gets surgery to look permanently hugely pregnant, by filling a sac or some other way like that. Does anyone have any idea that  story?

Sounds like Ericas belly
https://preggophilia.com/request-erica-s-belly-t