Are you on iOS 8.1.3? If so, go to Settings > iTunes and App Store. Click on your Apple ID at the top, then click sign out. Afterwards, sign back in, and make sure when you sign back in to type your email in all lowercase (e.g.
bob@gmail.com). Turn back on Automatic Downloads for updates after signing back in. If you're on cellular data only and don't have access to wifi, go to Settings > Cellular and ensure that App Store is turned on (but be forewarned that this will use up a lot of data).