It could be some of the hospital's board members who might not approve of their relationship and Cameron's pregnancy while working at the hospital. They could try to make things difficult for the couple.
Maybe a new doctor who has a crush on House and sees Cameron's pregnancy as an opportunity to drive a wedge between them. This new doctor could spread rumors or try to undermine Cameron during her pregnancy.
It could be the hospital's administration. They might oppose the idea of Cameron getting pregnant, either because they think it'll affect her work performance or because they don't want any drama in the workplace.
In Erza's world, there could be a dark mage who wants to use the power of the unborn child for their own evil purposes. They might see the combination of Naruto's ninja abilities and Erza's magic in the child as a great source of power and will stop at nothing to get their hands on it.
One potential antagonist could be Lucifer's father. He might not approve of the union or the baby, seeing it as a disruption to his grand plans or as something that could change Lucifer in a way he doesn't want. Another could be some of the demons from Hell who see the baby as a potential threat to their power or existence if it has some sort of unique abilities.
A rich and spoiled trainer who has access to all the latest Pokemon gear and rare Pokemon could be a rival. This person might look down on Cameron at first but later realizes Cameron's true strength. There could be a lot of tension and competition between them.
There are many fanfictions out there. You could start by checking popular fanfiction platforms like Archive of Our Own. Search for 'Cameron House' and then filter the results for stories that involve a pregnant character. Some might be centered around the challenges the character faces during pregnancy in the context of Cameron House.
Victoria Grayson would be a prime antagonist. In the 'Revenge' series, she was always at odds with Emily. If Emily is pregnant, Victoria might see this as a weakness and try to use it against her. She could spread rumors or try to harm Emily in some way to stop her revenge plot.
Ra's al Ghul, if he's still alive in the fanfiction, could be an antagonist. He might have different plans for Talia's future and the baby that don't align with what Talia wants. Maybe he wants the child to be raised in a certain way that Talia disagrees with, leading to a conflict between father and daughter.
The other gods who oppose the relationship between Percy and the goddess could be antagonists. They might see it as a disruption of the natural order or a threat to their power. For example, if the goddess is from a certain pantheon and her pregnancy by a mortal like Percy goes against their rules, those traditionalist gods would be against it.
The plot could be about a young woman in Cameron House who discovers she's pregnant and has to deal with the reactions of the people around her. Maybe she's worried about how the strict rules or the judgmental neighbors in Cameron House will respond.
One possible storyline could be that House, in his own complex way, realizes he has deep feelings for Cameron and secretly hopes she'll get pregnant as a way to tie her to him. Maybe he starts dropping hints or acting in a more protective manner around her.