Well, it might be time to check what charger you are using. If you have an iPhone or iPod touch, the charger for these devices has a much lower Wattage than the iPad's.
So make sure you are using the charger that came with the iPad.
But how do you tell which is which? If your charger looks like the image on the right, it will have some writing on it. If this writing shows a wattage value (10W or 12W), it is an iPad charger. The iPod and iPhone chargers are labelled with 'iPod' or 5W. (Below is an image of the writing on a 10W iPad charger.)
If you have a newer iPhone, your charger will look like that on the right. These new style 5W chargers are designed for iPhones, so will take far longer to charge an iPad.
But rest assured, you can use either charger to charge iPads and iPhones - the main difference will be how long the device takes to charge.