K.F.
I know exactly how you feel! I was so aprehensive about continuing to breastfeed when I came back to work. I didn't know if I would be able to do it, but it's a month and a half later and I still am.
First, you need to talk with your employer about a comfortable and private place to pump. It makes a world of difference to have your own space and not have to worry about anyone else waling in. I am able to use a locked office.
Second, make sure you pump for 10 to 15 minutes every three hours. I breastfeed at 6am, and I pump at 9, 12, and 3, then breastfeed my baby at 6 when I get home. The babysitter doesn't feed her after 3:30 so she will be hungry and ready to eat when I get home. When you pump, don't stress about getting enough milk. Pumps are not as efficient as the baby in getting milk, so you might not be able to get enough to feed your baby for a whole day. We have to supplement one feeding a day with formula. Just remember that any breastmilk is better than none! Oh, and it helps to have a picture of your baby with you.
Medela makes these pump wipes that make it easy to clean up your pump accessories while at work. Target sells them for about $12.
I cried all the way to work the first day I dropped my baby off at the sitters. Luckily, she loves the sitter and the other kids so it was easy to transition for her. And breastfeeding her when I came home helped us keep a strong bond. I was also worried about my employer being upset with me for leaving my desk three times a day, but then I realized that making milk for my baby was more important. It turns out that they have been very accomodating. (perhaps in part because it is the law)
After a couple weeks back at work, you will be in a routine and your anxiety will be gone. But whenever you feel stressed about it, don't hesitate to email me. I have been through it all and have wanted to give up breastfeeding so many times!