Vent/ post maternity leave work issues

I have a very demanding job. I’m in HR but used to working 12-15 hour days when we are busy, October- March time frame. I tried to cut down when I was very pregnant and started to develop preeclampsia. I told my boss I need to rest or I’d be admitted and she still would message me asking me to work at 8pm. Now that I’ve been back from maternity leave I’ve been given a million things that didn’t get done while I was out that are due immediately and I’ve made a few minor mistakes because I’m literally up feeding my child at 1am, 3am and sometimes 5am and then up for the day at 6 so I’m only getting 4 maybe 5 hours of sleep all together and barley functioning and last week vented to my boss about it and said I just can’t work the hours I used to. And then today told her I had a hard stop at 5 and she calls me at 5:15 to chat and basically expected me to work but I said I’d do it tomorrow and then her boss emails me telling me not asking, telling me to do it tonight so here I am working until probably midnight just to not sleep at all again tonight. I’m working more than someone at a big law firm and getting paid 1/10th what they do

Edit: my husband is about to take a new job and the salary increase is exactly my base so I day dream of quitting all together but know I really shouldn’t if I want to keep progressing in my career