In my experience, when I'm having problems focusing I find it's better to just put it aside and do something to ease my stress instead. When you can't focus you get irritated, it takes twice as long and you really don't retain any info so it pretty much pointless. Don't feel badly about it or yourself. Instead be proud that you can recognize when something is not a good idea and would be detrimental to improving your mental health. Although it's not always possible putting your mental health above all else is extremely helpful in getting better. If you do your reading another night when you can focus you will find it goes faster, you retain the material and you don't get frustrated.

Hope this helps. I know how you feel with both the reading and the FB thing. Hugs!