How do I quit my job?!

I’m a nanny and I commute an hour to and from work each day. The lady I work for has no idea I’m 20 weeks pregnant. And I’m just exhausted, driving so far is really wearing me out and the child has bad separation anxiety and I’m literally lifting her all day. She’s a single mum and the child is <a href="https://glowing.com/glow-fertility-program">IVF</a> and she struggled with fertility. I’m the only reason she has been able to go back to work and I feel awful to leave and she won’t be expecting it. I’m also hired through a nannying agency.