I work the same shifts, and I gave up pumping at work before I even started because I knew it was not going to work out. In the medical field, your breaks dont always mean a break. It usually means long enough to get sat down and get comfy then back at it hitting the floor running.
I switched DS to formula at 3 weeks old and he has been doing wonderfully. He is a happy, beautiful, well fed baby. I know "breast is best", but its not always workable in this day and age where all mommies cannot stay home with their babies, or work a sit down, 9-5 job.
You are a good mommy and that baby will love you no matter what you feed it

Keep your chin up!