i have the same pump...
i used it for a few months and then it slowed down significantly... try switching the plastic flap, ( the little white thing you get extra's when you buy the pump) i find these need replacing often cause they start to stick.... second make sure all the parts are put together properly and are nice and snug, this can also lead to it not working well. if this is your first time pumping it may take about 5-10 mins of trying to start milkflow- try turning up the suction and or speed this often helps
good luck!