Pumping at work

How often & how much do you pump? Yesterday was my first day back. I pumped 11 in the morning after feeding & 3x at work 7 oz each time. I was pretty proud of that. I came home & fed him twice. Then pumped for the night & only had 3oz. I used to have 7-8! I'm scared my supply will dry up but I was able to feed him.