You may not be signed into the correct App Store. There are different ones for each country, and you have to use the same one that you created your Apple ID in. Sometimes when you are looking at apps online and get redirected to the App Store, the store will change to the country for that link. Usually that's the U.S. store, since most sites tend to link to it.
There is no easy way to check this (that I know of). Your best bet is to sign out of the App Store, and then sign back in. You can do this in either Settings > iTunes & App Store, or by tapping on your Apple ID at the bottom of the Feature tab in the App Store app.
