...How did you know when it was time to swaddle them and put them down for a nap?

Our LO is only 4 weeks old, so I'm still trying to figure out her daytime schedule. So far it's a complete mystery to me. It seems to be completely different every day, so I have no idea when I should put her down for a nap. Instead, we just keep her out around the house during the day, and eventually she falls asleep on her own... sometimes. Other times she seems to get pretty over-stimulated, and she probably needs a nap. She'll fall asleep briefly unswaddled but then wakes herself up with her flailing arms. Many times during the day she eventually just ends up napping in the Ergo with me... but that means that I can't nap myself, since she is strapped to my chest. Babies are so confusing!

FWIW, she sleeps really well in her swaddle at night, which is why I want to start swaddling her for naps during the day. I just need to figure out when to swaddle her and put her down for sleeping...