Job issues

Okay, so I need everyone’s opinion on how I should handle this. I have worked day shift for about five months now, I am 18 weeks pregnant, my job randomly puts out the schedule and I’m scheduled night shifts.. with no warning, questions, anything at all.. so, I email my boss and ask her why the schedule was made this way, etc. she blows it off as I have to “float” now which means I work day and night shift. I have never worked a night shift, until now she knows I’m pregnant and will be taking leave soon.. I hate to play the victim, but it sure feels that way. I worked my night shift last night, I have been sick all night, on the toilet, my body just isn’t used to this and I don’t feel it’s healthy for me or the baby. I have another night shift tonight and I don’t think I physically can do it right now. They are not understanding and I worry I will lose my job if I call in..