This manga is about a guy whose ex-lover suddenly returned out of nowhere with a kid, saying that it's his child, and saying that after they broke up the ex-lover said the doctors found a hidden uterus and didn't tell the guy he was "pregnant"!! Does anyone remember this Yaoi!? 😲

doesn't seem to fit all of the things you said, but maybe Sex Pistols? In one chapter, one of the guys gets pregnant.

Look at male pregnancy!
Maybe you'll find it 😕

[img]https://31.media.tumblr.com/fed8f641faa089fa16ee883f5b18f006/tumblr_n09tpwWCYW1qk16e0o1_500.png[/img]
K n e e l .... This is the difference between your and my eye-level.
Rai from Noblesse

I tried that. And: single parents, lgbt parents, and childcare 😔

Kiseki no Koibito by Kisaragi Hirotaka?

Thank you sooo much! I was looking for it in the yaoi section. I didn't even think of the shounen-ai! 😀