2nd time mommas!

I know there are some second time, third time, etc mommas out there, so I have a question for you: HOW are you gathering enough energy to run around with your others and not just want to lay down and nap? I'm really struggling with it and feel like a half ass mom for even feeling this way! I work during the week, so I just want to spend every moment with my one year old that I can, as well! Help!