How do I tell my job

I’m 21 weeks and my sister just told me she may have been exposed to covid and she is getting tested in the morning. I have called out of work last week and left early this week for emergency for my pregnancy. I don’t know why I’m so afraid to tell my job I been in contact with someone who might have covid. They had the nerve to ask if I can wait until my shift to handle my emergency the other day. I hate feeling as if I’m unreliable but I am high risk and I know jobs are replaceable. I don’t want to also make it seem like I’m using it as a excuse to work.