So, the last couple batches of beer I've brewed have had problems carbonating. I suffered through two weeks' worth of pumpkin spice beer which was both bad (the yeast never really were happy) and flat, and also subjected a couple of coworkers to it; but I put my foot down when my IPA came out flat too, cause that beer is damn tasty.
One of the MCB guys suggested reagitating the bottles every couple of days, and that worked ok. Oddly, the 12-oz bottles have showed a different carbonation level than the larger ones, which tells me that my sugar solution didn't mix evenly in the bottling bucket.
So anyway, last night I opened one of the big 22-oz bottles of pumpkin stashed at the back of my aging cabinet. I'd agitated them too, and wonder of wonders, it had a puny little head when I poured it! And that made it a lot more drinkable, naturally.
Moral of the story: if you're wondering whether a bottle has carbonated, check if there's yeast residue settled out at the bottom. If there's not enough, turn the bottle upside down a few times to get everything agitated and leave for a week.