No longer recieving notifications?

Anybody know why I stopped receiving notifications? They were working yesterday for the most part but then sometime last night I noticed I stopped getting them even though people called me/replied to a comment of mine. Also when I click the little flag icon (or whatever it is) to see the old ones it says there are none even though I had a bunch just yesterday...anybody know how I can fix this?

@blade_r: if you look around you will see that this is a known issue, there's half a dozen threads about notifications around yours.