Back to work and supply down

I went back to work a month ago and I've noticed my supply seems lower than usual/I've regulated somewhat. I pump in the morning before work and nurse. I am only able to pump once a day around lunchtime since that's when I feel the most engorged and when I have time. I pump about 6 oz but have been pumping less and less over the weeks and am now down to 5 oz. My 3-month old also just started drinking more, going from 3-4 oz to over 5.

Is there anything I can do to jump my supply back up a bit? Should I pump more often at work even when my breasts are soft? When I'm not at work, I nurse constantly.