I love my kids but some days I feel nothing. Is this baby blues or something more?

I want to be careful with how I say this because I don't want anyone to think I am not taking care of them. I am. They are fed, clean, held. But some afternoons I sit with the baby on my lap and I feel like I'm watching myself from outside. Not sad exactly. Just flat. Like the volume of everything is turned down. Then Aarav laughs at something and it comes back for a while. It's been maybe 6 weeks like this. My husband says it's lack of sleep. Everyone says it's lack of sleep. Baby blues was supposed to be over by 2 weeks, na? At what point do you actually go and talk to someone?