Problems with Carbonation

I just did a Hefeweizen style wheat, one i've done before but flavor wise i got just right on this time, problem is the carbonation is way off, hardly there. I actually left the beer on the sediment after the SG dropped for about a week and then added the 1.5 cups of cooked malt syrup before bottling. i also moved the brew down into the basement at 55 degrees. I know that the temp could have slowed it down quite a bit so i brought it up and left it at room temp for another week.
Like i said the beer taste great, as we speak, actually went awesome with an orange slice since i didn't have lemon but could the brief hit to a low temp during carbonation and conditioning been low enough to knock out the yeast? Or could leaving it on the sediment for the extended period of time been a problem?

Any suggestions would be great since i already need to make another batch of this. The beer is about a month old right now.

I'm thinking the 55 degree basement caused the yeast to go dormant. I'd recommend gently turn them over end over end so any yeast cake on the bottom is all mixed up, and keep them at 70 degrees for at least 2-3 weeks.

I'm not sure what you added for priming sugar- what is 1.5 cups of cooked malt syrup?

How long has it been bottled? Malt tends to take a week or two longer than dextrose to carbonate properly.

sorry, recipie called for 1.5 cups of DME, cook it until it disolves in 2 cups of water, i just called the finished product 'cooked malt syrup' , that is what was used for priming

ok, i didn't know that malt took longer so i should probably bring the pig keg up out of cold and give her a shake too and leave it and the bottles in a warmer room for a good week?

At least a week, maybe more. It might take a good while to get them to carb up, depending on how active the yeast is now. Keep it at 70 degrees for at least a week or two, then check one and see if it's carbed up yet.