PND of course does exist, and if you think that you may have please do see your GP or HV as soon as you can.
However, I think that people can be very very quick to medicalise and label what are actually very normal feelings post-birth.
I felt for quite a long time (several months) that I didn't love DC1. his doesn't mean I disliked him. I thought he was gorgeous and wanted to look after him but felt that I was babysitting for someone else's very cute baby rather than that I was actually his mother. I never felt that lightning bolt of love you hear about, it was a much slower process for me.
I was very wary of discussing this however, as I knew that the first thing people assume (and they're right to check, of course) is PND and start pushing you into that box when sometimes its not the case at all.