literally! the only BL I've read that was bold enough to show the pregnancy and struggles was https://www.mangago.zone/read-manga/ookami_sama_no_ichizu_na_bouai/
Read A Tiger's Den. Although the seme is a horndog 24/7 omega is pregnant since the start until almost finish of the story. Oh! He also got pregnant by artificial insemination and not sleeping with the Alpha
Your gonna love this
https://www.mangago.zone/read-manga/making_a_child_with_a_beast/
Also Gentle Forest
not omegaverse just a sickly guy who became preggo because he have a womb
"Surge looking for you" has em, the omega went through quite a few struggles
Authors always wanna include mpreg but aren’t bold enough to draw them further into the pregnancy with a baby bump