Well done you! It takes a lot to open up and tell someone that you feel like that, when the whole world tells you that your life is perfect and you must be happy because you are a mum - I know.
I hope that your Dr is as good as your HV has been, so that you can start feeling a bit better, but remeber that it won't be instant. Maybe now your partner will realise how bad all this has been for you. Mine did once I'd spoken to the HV. I managed to tell him how he could help and what he was doing wrong. Things still aren't perfect between us but I no longer think he's totally useless and want to leave him.
Things will get better - take lots of photos of your little girl, and try to get out for a little fresh air every day, find something that makes you feel good, a bath, a book etc just make time for your self (mine is painting my nails, something I can do without thinking and then I have to sit still for 20 mins doing nothing, while it dries - bliss!!! Makes me feel better anyway) Also have a really long think about all the things your partner does wrong, pick just the most important ones and tell him - men aren't psychick they need telling (in my experince!)
I never went to see my GP - I chickened out! So I really do take my hat off to you for being so strong, stronger that I was/am. Take care xxx