I can totally relate. I had my second 3 weeks ago, my daughter turned 2 just shortly after DS was born.
I had moments of 'what have done?' in those final few weeks of pregnancy as I was also concerned about how things would work out. I was worried about how DD would handle the new arrival, I felt I hadn't prepared for the baby, I didn't feel as excited as I had before the arrival
of DD. However, the moment DS was born, I felt utter love and he's slotted perfectly into our lives. I'm really glad all my worries were largely unfounded and were just natural feelings of apprehension as life was about to change for us all.
I'm not sure if we're just very lucky but we seem more relaxed this time round and DS is a chilled baby. Yes, sleep is fragmented but we are working as a team. Every decisions made so far we've made from a family perspective.
Our DD has been really welcoming of DS and we've made sure she has plenty of attention. She's thrown some tantrums but we are doing what we can to make her feel validated in her feelings.
I ended with an emergency CS so have needed more help than expected, I had hoped for another vaginal birth but as births go, you cannot really plan. I'm currently in hospital again as DS had to be admitted with an infection on Sunday, so it's all been really crazy. But it's manageable and the overriding feeling is that we're a very happy family of 4 now.
I would say to just accept whatever feelings you feel, and not be hard on yourself. I did as many activities as I could with DD before DS arrived, cherishing that time we had as just the two of us (and dad of course) prior to our new arrival coming.