why is he is doing this?

my baby keeps pulling on and off the breast and it hurts nips are so sore....but if i pull him off he gets frustrated cause i think hes still hungry but then he also will spit out the milk idk whats going on but it goes on all night

My son did this and I figured out it was because I had an over active let down...I was drowning him when I would let down and it caused him to spit up/gag ect and he'd pull off without unlatching.  I had to pump a little at first to get past the initial let down and then he was better...eventually it corrected itself or he just got big enough that he could keep up better...don't know if thats the problem for you but its an idea.

MandyLou:

My son did this and I figured out it was because I had an over active let down...I was drowning him when I would let down and it caused him to spit up/gag ect and he'd pull off without unlatching.  I had to pump a little at first to get past the initial let down and then he was better...eventually it corrected itself or he just got big enough that he could keep up better...don't know if thats the problem for you but its an idea.