my 18 week old has become really fussy during his night feeds. We had managed to get them to a very efficient 20 minutes with little fuss but the last few nights he starts screaming after a few seconds and arching his back and won't latch on but then continues to scream because he is still hungry. I try to distract him by changing his nappy or putting him back to bed (in case he actually isn't hungry). It definitely feels like he is frustrated because my let down is normally so strong and seems to take a little longer at night - if he was a bit more patient it may only be 30 seconds or so! I have been able to calm him down by feeding him standing up or gently bouncing on the bed and then letdown happens and he is happy again. It has meant our nice quiet 20 minute feeds have become an hour long battle - which makes me feel guilty about keeping the rest of the house awake!
I tried hand expressing but I have never found that to cause letdown - just takes off what is currently in the boobs.