Solow - have only scanned this thread but had to post. Please go to see your GP or health visitor - you might have PND like my dp did - or you might be 'just' utterly exhausted and stressed out by the whole thing like I was..!
Either the first 6 weeks are complete hell and honestly your dd is just being a normal newborn baby. They're a nightmare and it's fine, normal and OK to think so.
I remember when ds1 was about 6 weeks old, wanting to kill all other Mums - why didn't anyone tell me I was about to enter hell?? I was furious everyone had kept this huge secret and someone should have told me it would be awful, stressful, and nothing would seem the same.
Honestly, it gets better - I'd say the next 6 weeks will get a tiny bit better each week, and then from about 3 - 4 months onwards you start to see little glimmers of life returning - usually after a decent night's sleep!
Life isn't the same again - can't be, but you feel better about it as you start to sleep more, eat better and get a bit of your old life back.
So please go and see someone re: PND - my dp had Sertraline and it did the trick within about a week. She was on a low dose for about 8 months and then came off it with no problems. And if at all possible, call in as much help as you can - day time help so you can grab the odd nap - or go out on your own, and evening help to maybe get out for a meal with your dh.
Good luck and there's lots of us here who've been through a very similar experience so keep talking!