Notification Centre Issue iPhone 3G

Just recently my Facebook has disappeared from my Notification Centre. This means I do not receive any notifications to my phone. If I'm on my PC, all notifications come through all the time. My software on both the phone & app are always up to date.& I had been having no problems until about 2 weeks ago. I've been into my app to account settings as instructed by Facebook but everything is ok & my partner who is also using an iphone 4, her settings are the same & she's had no problems.

I've tried uninstalling the app both on the phone & through itunes & then re-installed them, but only once did Facebook appear back into the Notification Centre & all that evening I was receiving the notifications, but the next morning when I switched on the phone Facebook was no longer in the Centre.

????