Parenting is so freaking hard

How do y'all manage to stay sane with 2 young kids? I have a 2.5 yo girl and a 3 weeks old boy. My life is miserable.

My toddler is the most demanding and determined kid I've ever seen (and others confirm that she's really really hard to manage, it's not only me). She'll fuss for ANYTHING and she's now super jealous of her little brother so she's even harder to manage. She also just broke her leg which will prevent her from walking for the next ~3 weeks (when not walking she's not in pain).

My newborn is an easier baby than my daughter but he's still a newborn needing to be fed a million times around the clock.

How do y'all manage to stay sane? I'm dead exhausted and I dread the thought that this won't improve that much for many years. I'm so exhausted that I even feel dizzy (doctor confirmed it's due to sleep deprivation and stress)

Edit: sending a warm hug to all of you for providing me with some much needed advice, reassurance and hope