I just don't know what to do for him, except continue feeding him when he wants it.
I posted a couple of days ago that he had a cold and was a bit snuffly, so was having problems feeding as much as normal, but at the moment he doesn't even sound snuffly - the stuff flops around in his tubes, so sometimes he's bad and sometimes not, IYSWIM. At the moment, he certainly seems to have a clear nose.
Yesterday, he was really unsettled for most of the afternoon and all evening, which is very unlike him - normally he sleeps like an angel on my lap all evening, feeding occasionally, and only at bedtime does he wake and have an unsettled hour or three! This was much more 'classic' newborn stuff for that time of day - crying, not settling to sleep whatever we did, not happy at being carried about etc, all evening. But honestly, it's the first unhappy evening he's had.
He was fussy all night and is still unhappy now - he wants milk and he wants the sleep that comes with it, but he latches on and off, sucks and nibbles at me but doesn't latch, and finally gets red-faced and yells in frustration. 
I think he must be getting enough to get by on, as I'm not noticeably engorged and he's not screaming in hunger (I think). But it's the fussy latching-on and off that is the problem - he just can't settle to feed happily, as he's normally done.
He has bad wind problems, always has done, and while it's no worse at the moment, perhaps he has a sore tummy and the feeding is just triggering tummy pains?
Any advice? I know it's highly unlikely to be 'something in the milk' but I'm beginning to doubt myself and my common sense (not to mention everything I've read!) and wonder if he's responding to something I ate in the last 24 hours. Not that I've eaten anything very esoteric or unusual for me, though.