Is there such thing as not allowed to take MC?

Hi all, I am working directly under my boss and I am the only person doing the job. In other words, no colleagues etc. Just boss and me. Supposed to hire 2 full time staff but boss hired only me cos she wants to hit KPI and have more profits for the coy (heard it from someone who knows boss). There were a few times I had to take MC but my boss told me she doesn’t want to cover me and i have to find someone to cover me if I want to take MC/and if I’m gonna die. A few times, had to resort to take urgent leave becos of this. Feeling v v v miserable at work, want to quit so badly without a job lined up cos it’s taking a toll on my mental health. Help.