Did your boss give you time off?

I'm a cashier at CVS/pharmacy and I haven't told my boss the actual situation, I just told her I absolutely could not work yesterday (due to contractions, extreme bleeding). How should I tell her what happened? I'm scared I will get fired for calling in "sick" at 4 am when my shift was at 8am. she seemed mad. because she didn't have anyone to cover me but there was absolutely nothing I could do. I couldn't go to work with blood gushing down my legs, doubled over in pain, right? This is the 4-5 time I've had to call in sick during the past 2 months because of this pregnancy. (morning sickness, cramps) Do you think she'll fire me? Any suggestions?