You just lost your mom. It's the bleak mid winter. We're in the middle of a recession and you don't have a job. You would be insane not to feel down about it all.
But you know intellectually that things change, and this too will pass eventually. It's hard to see that when there's so much shit right now. But it will get better.
Meanwhile, it sounds trite, but think about the positive things. It's hard to see them, but they are there. Your family. Your nieces.
And this also sounds trite, but are you getting enough exercise? There is a connection between mind and body, and getting moving will make you feel better mentally as well as physically. It's not a guilt thing. Don't feel guilty if you aren't active, just view it as an opportunity. At least one thing you can take control of.