Why can't my iPhone download apps?

[283]

I have an iPhone 4 it's on iOS 5.1.1 latest version and lately it takes forever to download and then it tells me that I can't download and to try again. Idk i downloaded some apps if I keep hitting the retry thing but I can't update instagram it says to keep trying again. I still have plenty of memory left my 3G is really fast right now so it's probably not a data connection problem (my Internet is lightening fast after midnight and that's when Im up download apps and stuff) anybody else having any problems like this? How do I fix it? I've tried turning it on and off

[ckm1956]

Start here. One of the steps usually works.

http://www.apple.com/support/iphone/assi...#section_1