pumping schedule??

For those who exclusively pump.. how often do you pump? How long do you pump for? DD is 2 weeks and nursing isn't going great, but I still want her to get breastmilk so I am pumping, but I don't seem to be producing as much anymore or as much as she is taking... I she been pumping after 2-3 hours for 15-20 minutes, but I want to make sure I'm not losing my supply