I like what the other moms have said so far. You say nothing has changed in your lifesyle--but it has: you now have an older child to chase after!
Remember to nurse, nurse, nurse, whenever baby wants to! That's the best way to keep up your supply.
Also check your pump. A tiny little leak in the suction can make a world of difference in how much you get. If it is a battery pump, try replacing the batteries and see if that helps. Or try a different pump, could you borrow or rent one for awhile?
If you haven't already, talk to your local La Leche League leader and/or attend a meeting, and/or check out their website. Remember, this group "wrote the book" on breastfeeding: "The Womanly Art of Breastfeeding" (probably available at your library, or you can sometimes borrow from the LLL group library, you'll get the most recent edition there--I read tons of good stuff that way).
I seem to remember there are herbs that help with maintaining supply but I forget what they are.
Remember to stay well hydrated--do you drink coffee/tea at work? those will dehydrate you if you don't drink extra water to compensate.
Sounds like you are doing a great job! Hugs to you, and hope that helps a little!
K. Z.