I'm not 100% sure yet but I had this issue, not receiving notifications (except for Words With Friends, weirdly) and I think I resolved it. I went into settings>notifications and for everything I had in notification centre, I turned off 'view in lock screen', exited settings and then went back in and turned them back on. Since then I've been getting a few notifications which I wasn't getting before, mostly facebook but also mail.
Try this, hope it helps.