Pump waayyy more in the mornings, is this normal?

El

So I just went back to work and started pumping when I’m away from my baby. In the mornings I pump like 12 oz combined from both breasts but after that I’m lucky to get 4-5oz combined. Is this normal. I’m pumping every 2-3 hours at work. Feeding her in the morning before I go in and all evening/night at home. Anyone else experiencing this?