I remember almost every last detail. The uke is isekai’d to a fantasy world by giving birth the king’s son and the king basically hates him because, before he was transported to another body, he was an arrogant prince. The king slowly started to warm up to him because of how much he adored their son.

It technically is not omegaverse and I believe it was an anthology series (series of one shots)

And I already tried searching isekai/male pregnancy or else I wouldn’t be here. Please help

I believe this is what you're looking for!

Thank you!