The other posters have given some great advice already. I agree with Karen that even though it is SO hard, exercise really does need to be a part of your plan. What kind of lunch break do you get at work? You could bring tennis shoes and go for even a brisk 10-20 minute walk, starting twice a week and working up to every work day. On the weekends you can get your family out (when it's above freezing!) and get active.
Even though you are very tired exercising will actually help improve your stamina. It is so paradoxical, but when you add exercise into the mix you will sleep deeper, wake more refreshed and have more energy when you typically would run low. Just try to get a few 10-20 minute spurts of physical activity in your day and work up to an increased frequency or duration. Weight training is something else that will really help - muscle burns more calories even at rest!
Overall, even though I lose the pounds in the first two months it took me the better part of a year to get back in shape with my 2nd daughter (I got pregnant 8 months after my first, so didn't lose it all with her). I just ate in a reasonable manner and did light exercise at first until I felt I could handle more. I took my girls on A LOT of stroller rides and I made it a point to get them used to it - it was for my health and sanity, after all! I even took them out in cold weather (not like this, though!) and bundled them up and off we went. I added weight training around 7 months and did that a few times a week with an exercise video. By the time she was almost 1, I was able to really work out hard and got much of my muscle tone back. It does take a while, so relax and keep at it :) While you may lose the pounds it takes a little while to get your muscles back into shape.
I would be wary of any 'fad' diet, regardless of what the ads or celebrities say. Any 'diet' needs to be something that you can live with forever or you'll just end up gaining all the weight back when you stop. Programs like Weight Watchers are wonderful for teaching portion control and healthy choices.
Hang in there!