First, HUGS! Being a new mom is HARD! And although your love for your child will forever be added to by what you went through to get her, it is making things harder right now. Like another poster said, you spent all of your energy wishing and hoping and terrified, not being entirely sure that this would work out, and the next minute you are a mom. Your emotions didn't get the prep time that bio-moms get. That works against you. Also, you might feel (and often other feel) that since this is what you wanted so badly, you don't have a right to complain. You asked for it. You don't have the right to feel unprepared, overwhelmed, or to say 'I hate this' - ever. I felt that way, anyway. Luckily for me, my dad is a family therapist, and helped me understand, and finally believe, that I have a right to all of the emotions/fears/stresses that a bio-mom does. Sure we don't get post-partum depression (which is caused by hormones) but many adoptive moms get post adoptive depression. And some of us just get plain old depression, caused by the losses, stresses, emotional roller coaster, and life-changing events, topped off with no sleep. Heck, the lack of sleep alone can do that for me.
One of the best bits of parenting advice I ever got wasn't even directed at my parenting... My sister had just had her first baby, and I was visiting to help, visit, and oooh & ahhh. I was a little stressed at meeting all of the needs, and not being able to fix every little cry. I would run and pick him up whenever he cried and try to make him stop. My sister told me, "You know, it's okay for him to cry. If he's fed, dry and safe, sometimes, especially if you need to be somewhere else physically or emotionally, it's okay for them to cry. It doesn't hurt them." That advice seems simple, but really helped me a lot when a few years later my daughter came, and was terribly colicky. I had moments that I felt I could not do this one minute more. It helped to remember that sometimes, when I needed to, if she was safe, then it was okay for me to leave the room, take a breath or a shower or whatever, and come back when I could love her better.
Good luck. Get some help. Not just so you can survive (although that is good enough reason) but so you can enjoy this time, too. Maybe medication short term, for a little while until your life re-stabilizes, or maybe just a good friend to come over when you need it. The first few months are the toughest. Give yourself 3 months easy before you expect yourself to be able to function normally.
My husband wrote a huge sign for me and tacked it to the fridge. It said that I did not have to have dinner ready, do any dishes get dressed, clean the house or say 'yes' to anyone for anything that I didn't want to until ____ (insert date when my daughter would be three months old). Well, things happened, and he later scratched out the date and added a couple of months.
And he was true to it - he did not expect anything from me during that time except to care for our baby. If I did do anything on that list he made sure to notice, except if I said yes to a favor, then he usually lectured me about getting worn thin.
I am susceptible to depression, and that was a tough time for me. Meds helped, and knowing that it would last for only a few months helped a lot, too.
Good luck. Please get help. And keep us posted on how you are doing! It's tough!!