My 2wk old DD has gone from being a peaceful sucker with a perfect latch, to now barely opening her mouth, and after 3 mins of sucking, shakes her head from side to side roughly (with nipple still in mouth.. OUCH!) and then pulls off, screams at me, I re-latch her, and same thing again.. and again and again, and then she just gives up and falls into a grouchy, agitated sleep. It just started in the last 2 days, though we had a lovely feed this morning (still with very lazy latch). Can anyone explain what's going on?