I'm four months in end of life, and yes, you do hit patches where you think how the hell am I doing this.
Have you spoken with your siblings about how you're feeling? Is it too much for a single person to cope with at a time?
It's very hard trying to keep a semblance of normal life going while nursing someone at the end, especially when it's so uncertain.
All the advice I can offer is to strap on your own oxygen mask first, get outside every day, take a brisk walk around the block, have a cathartic weep, talk to people and tell them what is ACTUALLY happening (don't bother sugar coating, this is for your benefit not theirs).
This is tough, I'm sure you've also had moments of small solace over the last month, I've used them as crumbs to keep going.
A month in all your adrenaline reserved will be well burnt off, so find a way to either replenish and recharge for a day
Or take every shortcut you can think of.