Possibly it's been a little on the cool side which is why it's taking longer. I presume your hydrometer readings are still dropping or are you going off the bubbling action?
Take a reading with your hydrometer to see where it's at, looking for bubbles either in an airlock or on the surface is unreliable to determine if fermentation is complete.
As Battwave said if the brew is stuck then stiring it might help to restart the yeast, have a read of this thread