Check out this link above. APparently hormones caused by lactation and letdown can cause negative emotions, including anger. I might guess that you're angry and upset about your situation (completely normal) and the pumping is just another reminder? I hope you feel better soon, but the link above may help you realize the whys and hows?
When I was pumping for my son, who had latch issues until he was about 6-7 wks old, I tried to distract myself with a "me" book or magazine not related to parenting, nursing, or pregnancy, or I watched a dvd or tv movie... the distraction helped the time go by and gave me some needed me-time. I used a hands-free setup (basically rubber bands that go around your nursing bra straps and hook over the horns) so I could also have a snack or drink at the same time.
2005: PE/IUGR pregnancy with Daughter, born 40+2 induction. Diagnosed with Sensory Processing Disorder (or Sensory Integration Dysfunction) in 2010. Diagnosed with ADHD in 2011. It's getting better with OT and treatment!
2009: PIH pregnancy with Son, born 38+5. Diagnosed in 2011 as Developmental Language Delays, Social-Emotional-Communication Delays. More testing Nov. 2011.
2011: I'm undergoing neurological testing. Praying for the best!