I need advice, I have a job in an assembly type plant and we work 12 hour days 3 days one week then…

I need advice, I have a job in an assembly type plant and we work 12 hour days 3 days one week then 4 the next and I thought I could keep up with it but it's really starting to wear on my body. I need the money but I'm physically strained at work and I feel exhausted all of the time. I'm 12 weeks pregnant also but my work doesn't know that. I've only been there for about a week. What should I do?