Packing whole day long

Going on a vacation should be a pleasant thing. But I hate packing! Itcould take me whole day to pack even just for a two weeks tour. I always pack until midnight the day before I leave...shame..shame...shame.
I have no ideas why it's a difficult task for me but i just couldn't concentrate on planning what clothings I should bring along even I've checked the weather in destination.
Anyone has better suggestions for me to ease my "pain" ?!