It may be that he's gotten a lot more efficient at feeding all of a sudden - his crying and fussing could be a reaction to you trying to get him to have more. I would definately watch his output and other signs to ensure he is getting enough - just in case.
If he's taking enough then your supply will be sufficient.

It could also be reflux (silent reflux even), wind or something like that. Or maybe you have a forecful letdown and he's having trouble with it. Personally, when in doubt I go and waste the time of my GP or CHN, just for reassurance. So far there's never really been anything wrong, but you never know.