Everyone will, at some stage of their PhD, get depressed and unmotivated IMHO. I am currently at the end of my 2nd year and I have been quite depressed in recent weeks despite the facts that I did have a clear goal and routines to achieve that. Maybe it's just that you get a little bored because of the narrowness of the topic you are looking into. While a PhD requires us to concentrate to maximise our energy on a single spot, it would still be better to look around at times to avoid the burnt marks that would have appeared on your retina, and to get fresh sights, i.e. ideas.