EP: How do you increase your supply?

Mine is tanking.........!

I think I let a little too much time go in between pumps gradually.  I used to religiously pump every three hours, but after going back to work I had to stretch it more and more.  

Now, my supply is down a few ounces each side every time I pump.  I used to get about 3 on the left and 4 on the right every time I pumped and now I barely get 3-4 ounces combined.

Any tips would be appreciated!