If you are storing your bottles in the 60's, and depending on the yeast strain, this could be your problem. After bottling, it is best to leave your beer at 75F (or even a bit higher) for the first week or two, and then you can cool them a bit.
Also, if you use a secondary and the beer is really clear when you bottle, there may be little yeast left in suspension to carbonate the beer. It will always happen eventually, but I have noticed that the longer my beer sits in the secondary, the longer it takes to carb up. This makes it even more important to follow the point above about keeping it warm.