Depressed during early pregnancy?

I'm very early in my pregnancy and I'm suddenly very depressed. I have wanted nothing more than to be a mom and to have children my entire life... and it's like, now that I'm getting that, I can't even enjoy the excitement because I'm so sad and I don't know why, and I'm terrified of things that I already thought through before we started trying. Like I know this is what I want. It's what I've always wanted. But now there are fears about pregnancy, delivery, and even motherhood that were never there before. I'm questioning everything. I'm crying constantly and I don't feel like myself at all... Someone please tell me it's my hormones!