At the start of the pregnancy, Izuku didn't think it would be that tiring later on.

But now, 6 months pregnant, he's tired out of his mind. Yes,he has the pregnancy glow,but that doesn't mean it makes him feel better.

His instincts are haywire, his body has changed slightly (obviously), he's more vulnerable,etc.

That's why Katsuki is going to take care of him.