What should I do?!

I

I’m 24 weeks pregnant and work as a retail supervisor. My shifts are extensive and physically straining for me because I’m on my feet for 8 to 9 hours a day without proper breaks. My one request is that I don’t work truck day because there are plenty of other people capable of working and it’s a lot of heavy lifting and physical work. It’s exhausting for me to do and I’m normally in a lot of pain after my shift is over. My boss keeps scheduling me for truck day anyways. Now she’s cut my hours and the only way she’ll give me more is if I work truck day... I don’t know what to do at this point. I’m beyond frustrated with her.