How much are you pumping at work? And how often are you pumping?
I have had this same problem this time - I expected to pump 3 times a day at work, I'm away from baby for 10.5 hours. But I went back and I was pumping at least 4 ounces extra per day than she was eating - and I wasn't pumping until the milk stopped coming out. I would pump until I got freaked out by how much was in the bottles. So then the next week I decided to just pump twice per day and that has been working out ok. I'm still engorged on Fridays (I work tues-thurs) and by Saturday I am not engorged anymore.
I also make sure to pump through an entire let-down and until the milk stops coming out because I'm worried about a foremilk/hindmilk imbalance.
Lilah 10/08 nursed 25 months
Beatrix 01/11 nursed 30 months