After about 4-6 weeks of doing the same activity all the time, your body gets used to it. So your job is just a normal part of your day, and additional exercise is what's going to challenge your body and help with weight loss. I wouldn't count your job as exercise, but you might need to adjust your calorie range to account for this extra activity. Here's an Ask the Expert that helps you figure out how to do that: www.sparkpeople.com/community/ask_the_expe
As far as your feet go, I would suggest going to a specialty running/walking store to be fitted for shoes by a professional. Even if your shoes are fairly new, if they aren't the right shoes for your feet they can give you all kinds of problems.
Hope that helps,
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford