At this exciting time in your life knowing that you have to be back at work can seem somewhat depressing and maybe make you feel somewhat guilty. A good thing to remember is not to dwell on it and prepare to get back to work slowly. Right after my child was born I was frightened of going back to work. Would I still fit in my clothes, be able to sleep at night and would I be comfortable pumping at work? I just wanted to cry knowing I couldn't be with my the baby.
If health issues are involved the weight may come off somewhat slower. See your doctor for advice.
Carefully go through all your old clothes and donate the ones you won't wear and wash up the ones your keeping. Before you go back to work take some time to try on all your work clothes and separate the ones that fit and don't fit.
On the sleeping - that will come with time. If your child wakes up frequently at night, it can be very difficult. Go to sleep earlier at night and try to catch up with naps on the weekends.
Issues of pumping-talk to other mothers at work and see how they did it. If you're worried about pumping at work talk to some of the other moms to see how it was done. If you do have a mother's room at your workplace try to touch base with the mothers currently using it. Get some input from them. Whatever you do, don’t dwell on your return to work while you are on leave, because you don’t want to ruin the time that you do have with your baby.