night time feedings

My 6 week old seems as if he's not getting enough milk at night when I nurse him. He's full throughout the day but at night after he nurses his normal 8 mins on each side (with burping inbetween and after) he's very fussy. Also sometimes during the day he'll get antsy while nursing. Arms flailing and turns his head side to side. So I assume he doesn't want anymore but then cries as if he's still hungry. Any suggestions? I don't think it's acid reflux, Doctor didn't suggest that either..thoughts?