Parents aren't meant to do this alone. Children are a common good, for one thing, so it benefits everyone to help parents raise children. And this whole nuclear-family-one-or-two-adults-alone-in-a-house-with-children-24-7 thing is extremely new historically and totally maladaptive, IMO.
So ask for help when you need it. Ask for help before you need it.
You may be emotionally hurt by parenting, or lonely, or just done. That's all normal. A chat with a friend or relative who loves you and will let you vent without telling you to be grateful can be just the thing to give you the strength to get through bedtime. Reach out when you need validation, commiseration, or just someone to tell you they like you.
If you have a partner, make sure your partner gets as much of a chance to do childcare as you do, so they can develop their parenting skills and form a bond with your child that doesn't go through you. And then if you're feeling fried, you can ask your partner to wrangle the kids while you recharge. (If you're being proactive, you'll work it out so each of you gets alone time regularly, so neither of you gets to the fried point.)
And whether you have a partner or not, you should start building a support network of friends and neighbors you can ask for help sometimes. If they like you, they are probably willing to take your kids for a few hours while you go to an appointment or recharge. But they probably don't think to offer, so you don't know until you ask.
Parenting is long, hard, tiring, occasionally demoralizing work. You don't have to white-knuckle through it alone. Reach out, whether you need emotional support or the physical presence of someone else, and your friends will be there for you. You don't have to do it alone.