Oh, I wish I knew what to say to you! I can only tell you how much I understand what you are going through. It's like living in a permanent haze sometimes isn't it? You often wonder if you are still awake or asleep. Just take one day at a time. My 3 year old dd is to do 5 mornings a week at nursery in Sept - not my choice but something to do with funding! I wasn't happy about it at first, but now I realise that I will need that time to relax and to adjust once the new baby is here. And I think she will enjoy it, I can no longer provide the stimulation she needs 24 hours a day! I have spoken to her about the nursery and she has been to visit, so far she seems fine about the idea and I think, is looking forward to it!
So don't feel guilty. She will have a better time there than stuck at home with you - I know mine will! There are days mine has literally been watching tv most of the day because I've not had the energy to get out of the house, or pick up the phone, or even to make dinner sometimes, so she has jam on toast. I'm not proud of that, which is why I think she will benefit greatly from nursery.
Try to keep yourself busy, make yourself appointments, book yourself in for Yoga classes or something, a commitment that gets you out of the house once a week. There is nothing worse than succumbing to the depression and staying in, no matter how lethargic you feel. Once out there you will begin to feel tons better, I promise you! Go the library too, get yourself some books to read to stop you from thinking too much. Ask for a CPN, they will often come to see you once a week, and it's another person to talk to, you need human contact! Your weeks will go quicker if you fill them up, so start making arrangements now.
I wish you the best of luck. Please let us know how you get on, and you can contact me via my website any time you like, the link is a couple of messages down.