By way of disclaimer, I don't really have the problem OP describes; don't really even understand it.

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.

You might also find that a different cadence than 25 minutes works better for you. I personally use 90 minutes because I find that if I make it shorter than an hour, that the timer is just an annoying interruption.