Work stress while pregnant

So long story short, me and my coworkers got way behind on our workload a couple months ago because we've had a lot of turnover and people quitting. Well so now that I'm asking about maternity leave, all of a sudden it's a huge problem that my work isn't caught up. I'm not the only one behind, but I am the only one getting reprimanded about it. So I spent these last two weeks busting my ass and did a month's worth of work in two weeks trying to get caught up, and got a whole bunch done. I even gave them loads of free time working at home to get it done. So today comes and now instead of commenting how much I was able to do, now more is being asked of me. What they are asking is basically impossible. I would have to pull 16 hour days to get done the amount of work they are wanting done... And if I don't get it done, they want to fire me. All while being 30 weeks pregnant! I'm exhausted after basically killing myself these last two weeks to catch up, but that wasn't good enough. My body hurts, I have tension headaches everyday, I physically just feel awful. I don't have it in me to give them the hours they are requiring right now. My only options are quit or be fired. I can't survive without a job 2 months before the baby is due. But I don't know how to survive 2 more months of working myself to a bone like this. The stress is unbearable. Help!