I had the same feelings after my first miscarriage. I analysed every little thing trying to find something I had done which had caused it to happen. I blamed myself even though everyone said that it wasn't and it just wasn't meant to be etc etc. Even now I still think that there is one thing I did that caused it.
I think it is human nature (especially for women) to blame ourselves for what happens. After all, it is our bodies and our decisions which affect this little person. Everyone will tell you that it wasn't your fault, it just wasn't meant to be and in time you will come to believe that, but I think there is always a part of us that wonders "what if I hadn't......".