sleep patterns

This is my third child, but I totally forgot when you could stop waking them up to eat. She’s 6 weeks old and typically eats 3 oz every 2-3 hours during the day and then at night she just wants to sleep. I wake her up when it’s been about 4 1/2 hours, but I swear if I didn’t she’d just sleep all night. It’s so weird. My other 2 cried all night(boys lol). I just wanted to know when it’s okay to let her sleep longer?