I'm joining this thread as I'm in the same boat as OP, and other posters it seems.
Five years ago, I had a full-time career, a fab social life, and a great wardrobe as I was a steady size 10.
Now though, I've had two DC's in two years, gave up my job to become a SAHM - and have put on 4 stone
. I feel bored, boring and tired. Lost all my pizzaz about myself - none of my clothes fit, and I hate going out clothes shopping, as I can't accept the size I've become.
Am also on Citalopram for PND, so libido went out the window long time ago, although this may be partly as a result of my post-baby body. DH hasn't said anything negative, insists he still thinks I'm beautiful, but I look at myself in the mirror and know deep down that can't be true 
I know the theory behind weight loss, but I just seem to have slipped into a rut of MNing in my jammies in the evening eating chocolate, drinking wine etc.
So, OP, I can relate fully to how you're feeling - and would love to join a thread in the vein of Positive Thinking 2011. I'd like to make it the year I actually get off my fat arse and do something about this - instead of just good intentions but no action.