My 5wk old DD is gaining weight and thriving, but when I express (which I can only do at 3am and 5am coz that's the only time they are full enough for the pump not to hurt) the most I can get is 40ml/1oz bfore my hand gets too tired and the milk comes realy slowly. Is this normal amount or should i just keep pumping? Will it make a difference if i buy a different pump???