pumping but no milk comes out.

so I am literally driving myself crazy trying to pump. I breast feed my 3 week old but I also have to supplement with formula, I was pumping an amazing amount and now that she's on breast more I try to pumo when she's asleep so that when I go back to work there is enough in the freezer. but when I pump nothing comes out. in an hand express it and loads come out. what am I doing wrong. how can i fix it. my boobs hurt!!! this is all I got...the last time I fed was 530 this morning she woke up at 830. and I fed from the right side. and she didn't want anymore so around 930 I pumped the left side....what am I doing wrong.