Hi OP,
I can't change your situation - wish I could. Shit pay, being knackered, feeing low all the time, these are things that really are hard to pull back from.
I used to suffer long term depression but haven't for about 5 years. I did take anti-depressants, and if you don;t I strongluy recommend you try some for a short time, just to give you a rest from the constant down.
These days, I find early intervention with CBT techniques work for me. So if I start feeling really low, I'll interrupt myself and say: take a break from feeling anything at all. Just breathe in and out. You don't have to do anything more.
It also helps me to take a big perspective. I am just a grain of sand in the universe - my time here is short and my importance is tiny. I don;t matter, except to DC. And that let;s me off the bhook from trying to matter, trying to be better at earning money/making friends/ being productive/slim/whatever.
you are allowed to just be. You are important to DC and you don;t have to be anything else at all. Ever. Let yourself off the hook for all other things.
Yous ay small things make you feel better temporarily. Try to stitch them together. If a walk or 10 mins yoga with Adriene makes you feel better in the moment, do it and then make a cup of favourite tea that feels better in the moment, and then play your favourite songs while you chop carrots to feel better in the moment, etc, until the tiny uplifts stack up a bit more often than they used to.
The other things that help are to give yourself a LOT of praise. I'm so much more self-c ompassionate than I used to be (used to be like living with the worst school bully/abusive partner 24/7. there was a raging war n my head.) But now I often catch myself saying, 'See, you thought you'd been a lazy arse on MN all day but actually you fed cat/DC/birds, did laundry, finished a report and mailed it, prepped tomorrow's meeting, baked some bread.' Doesn;t matter if all those things took 30 minutes in total and the lounging on MN took 3 hours, I still did them, even though I felt low and shattered. Well done. Little back pat.
When you start being self-compassionate, it almost feels revolting, so false and pathetic to congratulate the small stuff. But it does creep up on you and you find yourself just being kinder.
Last thing that helped me (and I appreciate you feel exhausted from trying so many things) but it did help, was just do something you've not done before, however small, every day - tune to a silly europop radio station, buy some Poundland sweets you've not tried before, walk down a street you've not been down before, play a card game with DC you've not done before, do a 5-minute workout online with a trainer you;ve never heard of etc etc. And just make a note of your opinion of the experience in a notebook or on your laptop. Anything you enjoyed or felt even a bit engaged by, do it again.
Long term, this attitude of being open to new experiences helps you have courage to take bigger chances with life - apply for a bette rpaid job or something else that will genuinely improve your situation.