So hang on. Do the basics of what you can do in the time you can do it, and give yourself a bit of a break over what you can't control. Maybe even work towards forgiving yourself and accepting that although it's not pleasant this is just the way things are right now. The important part to remember is that this situation/mood/feeling/experience is temporary, and although it sucks, you can move through it, and mostly likely will.
So hold on tight, and keep going. Remember when you are climbing a mountain, sometimes it can feel like you are staring at a wall of massive rock, but just take a moment to imagine the view from the top, and how you'll feel when you get there. You can do this, just keep going.