Janine, please don't think that you are giving up too easily. You have done a fantastic job to express for so long. I struggled to express once or twice per day in the early weeks, and my DH was home to help. You should be very proud of what you have managed to achieve.
Guilt is something that goes hand in hand with being a parent and will always be there. As MR said, think of it as a success because it is. You have given Emily the best start possible, so please don't feel as though you have failed.