This is a quote from a Gwyneth Paltrow interview where she talks about her miscarriage:
"It was awful," she told the Daily Mail's You magazine. "It happened really late, and I wasn't expecting it at all.
"For a long time I just couldn't understand that it had happened and why. I was like 'But I can't not be pregnant. I'm already past the first trimester, and I have three car seats in my head.' To this day I feel like I'm missing that kid. But it wasn't meant to be and you have to trust the universe. "
What does she mean by saying "I can't not be pregnant?" Is this "can't not" construction a grammatical and common usage?