Depression? Long, but advice please!

I am 3 weeks pp and before now I felt very happy and excited to have my baby here. I didn’t feel stressed or sad or anything. However I did notice This last week or maybe even sooner I’ve felt a disconnect toward my step daughter (I know that it’s not okay and already feel guilty, so please don’t bash me) I also would like to add that I haven’t treated her any differently or been mean or anything like that. She’s only with us 3 days of the week but I felt high anxiety and stressed when she was around with the baby. Its hard to explain but she acts out often and her father just let’s it happen. Instead of telling her to stop he makes excuses for her. She will be 4 in less than a month.

Just for a quick idea of what I mean, she was using our baby’s car seat for her doll. I told her she could keep her doll in there until it was time for us to go because the baby would need it back and she was completely okay with it and seem to understand. However her father took her doll out and said it was time to go and she started screaming her head off and crying because she didn’t want her doll out of the car seat even after he was trying to explain to her that we need it for the baby. He does nothing more. I brought up how I was surprised at her actions since she seemed okay when I told her that she could use it til it was time to go. He just told me that it was his fault and he should of asked her if it was okay to take her doll out.

I tried to nicely talk to my so about the way I felt but he took it the wrong way and we have been fighting a lot this last week over it. Now I feel anger and sadness and disconnected from him to the point where I’m ready to call it quits and leave. I have so much anxiety being home and feel like I’m suffocating. Is this normal behavior on my part or could it be pp depression? Maybe I am over reacting? But I truly feel like he needs to be more stern with her at times instead of letting everything go.