Having a Pomodoro [1] app on your desktop/laptop helps. It sounded lame to me initially (do work in 25 min chunks), but it seems to work for me.
But I'll second pomodoros for pushing productivity and focus without killing yourself.
I'll add that daily exercise improves clarity of mind (read: more focus and other benefits). And having a busy schedule limits my ability to spend time on social media or sites like Hacker News; so when I do spend time on them, I tend to be more efficient with it (i.e., focus on those things most important to me) and feel like I get more out of it.
I think that last bit may be part of the problem for OP: the reward becoming harder and hard to get, requiring more and more time. Going cold turkey and then slowly introducing Facebook et al., back in might help a lot.