I feel the same way, and my pfb DS is 19 months now 
We had been TTC for almost 6 years. I think that an experience like that can make you feel blessed when you get pregnant at last and miraculously you have a real baby! I made a conscious decision to enjoy every stage rather than wishing him onto the next milestone. I think this has helped me live more in the moment, made me grateful for what I have and I am a much happier person.
It is absolutely fascinating to see every new thing he learns (not just the big milestone moments that you imagine) all the little tiny things you notice about him because your his mum/parent.
I'm not saying I never have negative emotions about life as a mum but they are very small in comparison to all the awesome bits so far. I know not everyone feels like this, especially if they are hit by PND.
I think sometimes people have busy, social and/or professional lives and can feel isolated by motherhood. Personally, I felt isolated before motherhood and was only beginning to recover from severe depression and anxiety when I got pregnant. And my confidence has come on in leaps and bounds since having DS. (Not necessarily just because of him, but because of learning things about myself, realising that I can do much more, much better than I thought I could). I meet more people, and have done more things outside being a mum than I did before I was one if that makes sense?
So I have sympathy with those who struggle with motherhood, as I struggled with university and work. But for me, becoming a mum has helped me figure out who I am and become a better person. Other people find this confidence through work, hobbies, education or seem to be born with it, so I'm not saying people have to become parents to 'find themselves' or that parenting is that thing for everyone. For me it was. :)