It actually depends on author who they wants to get pregnant in omegaverse.. If you read Okusama wa alpha manga, it has a married alphaxalpha male pair and they have a kid in the end. In Kashikowarimashita, destiny the second pair, alphaxbeta male couple, the beta gets pregnant at the end and they have a son. It also have a alphaxbeta female pair and the beta gets pregnant.. Same with gender conversions..There is tons of variety..
Yeah, no prob.. the sole reason they change genders based on situations is bc they wanna show bonding which only happens between an alpha and an omega.. the other genders can be together and even have kids but bonding is something exclusive to an alpha and an omega pair.. so if they want bonding/soul-mate kind effect in their story one of them i.e.the uke got to convert into an omega or if the uke is already an omega then the seme got to convert into an alpha..
Why cannot stick the idea he is an alpha? Becoz alpha x alpha also can get pregnant. It's just low birth actually. The cover still had a x a so I want to believe he is an alpha. It's just that maybe that a hint of his pregnacies. In omegaverse anything can happen depends on author's will. Sometimes there are many different types of omegaverse world made by author but general idea is still there. If we can see in this manga show that alpha x alpha cannot be bond but others comic can.
He vomit maybe becoz he make a bond and pregnant. Sometimes it's made me confuse becoz of the different idea of omegaverse world (I mean the little info that made up by author). So in the end, I made conclusion in omegaverse world anything can be happen.