I think you should speak to a midwife or your GP for some advice and support. It might be baby blues but it does sound like you’re having a hard time of it and would benefit from some support.
I had this a few days after day 3 but it didn’t last very long. I’m on day 14 now and still getting quite a bit of anxiety but it’s more relating to whether I’m doing things right. If it doesn’t pass quickly then definitely talk to your health visitor or midwife. Or call them right away if you think it would be helpful. I have been talking to my partner and mum whenever I get upset. They’ve given me a lot of reassurance which helps!
Could be but I'd recommend reaching out to GP or midwives for support in any case. CBT and counselling are both good treatments for low mood