This is why therapists often highly recommend gratitude journaling. I've never been a fan of the 'gratitudec name of it, but the basic idea is you make a habit of writing down (and thus deliberately paying attention to) the positive and nice things in your life, and that counteracts negativity bias and makes you notice the good things more. Even when your current situation is awful, you can still find stuff, like a nice sunny day, or a friend giving you a compliment, or a cool fact you learned, or a tasty scone and suchlike. After a while it becomes a habit to pay more attention to positives even when you're not writing it down.