Hey everyone, right now we have a little technical 'SNAFU' which means that notifications (the little icons that indicate whether you have new PMs, or have been mentioned in a thread, etc) are missing in the user menu (the top right pop-out menu).
We have a support ticket in, and hopefully we'll get it resolved soon.
In the interim, you can visit your Profile by clicking on that pop-out menu and clicking 'Profile', of course. There you can see your notifications feed, if you scroll down a bit.
In addition, I've added a private messages box to the right hand side of your profile page too, which will help you get to PMs.