job not following doctors orders

Brittany
I am a waitress and I'm 18 weeks pregnant. My doctor wrote my job a note saying I can not work more than 8 hours a shift and I must take my break in the middle of my shift (rather than the beginning of my shift as they make us do). When I gave them the note everything was fine no issues but now they are disregarding everything my doctor wrote. Any one of anything I can do about this?