Meeting with my boss


So I'm 29 weeks pregnant and I'm a retail Manager working 40+ hours a week. Last week I worked 50+ hours on a 6 day stretch. I recently spoke to my boss about changing my schedule to only 1 closing shift per week due to me getting further along and I'm doing a lot of walking causing stomach pains/contractions. She explains to me that she cannot do that because the other girls will get mad that they would be closing all the time. She then decides to schedule me 8 days in a row at 70 hours. I told her absolutely not! I explained that I can hardly manage 50 hours with the pain that I'm having and that will literally kill me. I told her that I'm trying to work all the way up to 38 weeks and if she continues to schedule me like that I'll end up on bed rest and won't be back until after I have the baby. Well guess what! After working 50 hours I went to my doctor because I couldn't walk/ sit/ bend/ or even wipe my own ass.. I was put on bed rest for 5 days and guess who was mad they had to cover my shifts. Tomorrow is my first day back and I want to have a meeting with her about putting me on a set schedule and if she cannot do what I need I'll be using FMLA and leaving at 35 weeks. How would you discuss this situation with your boss? I really do not want to go on Maternity leave that early but I feel like I have no other choice. She's constantly scheduling me until 11 at night and I'm so exhausted.