IOS 6.0.1 facebook notifications problem(bug)

I've iphone 4s (IOS 6.0.1), and my problem is that my notifications aren't working with facebook app, i don't get notifications on closed screen, and when i use the phone. what is that? how can i fix it? what should i do? Please help me, i've just bought my phone 2 days ago... and its not good reason to buy a new one..i guess this is a bad start to meeting the apple.