This might not be the story but it's very similar in novel to the one you mentioned
'Living as a extra in a BL Omegaverse Novel'
YESSS THANK YOUU ε=ε=(ノ≧∇≦)ノ
Salt society
This is not it, but thank you anyways!! Will read this as well heheheh thanksss ヾ(☆▽☆)
No worries, i almost mistook this work as the one you're searching for cause the mc is pretty stoic too in this one too lol but it's not yet manhwa so gotta wait.
I'm trying to find this one manhwa about Beta who doesn't know that he's becoming Omega. He had intercourse once with the Alpha and got pregnant right away. The manhwa is ongoing and latest chapter i read like 2 weeks ago is at part where the bottom has a morning sickness. I think the bottom is quite nonchalant and stoic about everything. I cant remember anything else about the plot cause everything was too fast under 20+ chapters ╥﹏╥
p/s: i feel like i already bookmarked this under 'I want to read' but not sure if its gone/glitched?