under carbonated beer - how to fix this?

I just popped open my first beer out of a batch of tripel I made. The taste was right on the money. However, the carbonation was very very weak. I think it was due to the fact that I did a 40* secondary which dropped most of my yeast and I probably didn't re-incorporate enough of it at bottling time. However, I know there was yeast in there during my bottle conditioning, because the bottle had some yeast at the bottom.

primary - 30 days
secondary - 30 days at 40*
bottle conditioning - 30 days at room temp

how do I get these things more carbonated? Do I turn each of them upside down and shake them to get the yeast back into suspension? Do I have to open each one, put them all back into a 5 gal bucket, and start over again with more yeast and more priming sugar and 3 more weeks? Thanks everyone.

I have a belgian golden strong (1.090 Original grav) that at 2.5 months is only now starting to carb up...your triple is a high grav beer, it's gonna need more time. Just roll them gently on a table top to re-rouse the yeast (you don't need to shake) and put them away, they will carb up eventually....

but the higher the grav, the longer it needs to carb and conditions....