Long term, therapy and medication and taking care of yourself. It's tough, but with a lot of work you can start to figure out the pieces of it - which parts are physical/environmental, which parts are mental thoughts patterns and changeable with therapy, which parts are chemical and need the right medication. They all feed into each other, of course, but after a lot of years and work I've gotten a pretty good sense of which part is my "chemical" depression which changes with medication and which parts are modifiable by me.
Of course, that all takes time. In the short term, first, do a health check: make sure every day fhat you've eaten, you've drunk water, you've slept, and you've gotten some sunlight and a bit of a walk at least. These are not cures but they are compounding factors. If you're depressed and hungry and exhausted the depression is going to be magnified a lot more than if you are well fed and rested. Then, do your best to stop thought spirals. If you don't want to be alone with your thoughts, find a podcast or YouTube channel or show that you like and always have it on. Listen to that instead. If you have a hobby you can do that doesn't rely on making "good" results or being inspired, do that (for me, I learned that I can't write or draw while in depressive spirals because I'll start thinking everything I make is trash and that makes it worse, but I can play the piano and practice songs I already know - figure out what works for you). Again, this isn't a fix, but the goal is to stop any spiraling thoughts from getting worse. Do whatever it takes to distract yourself - "ignoring it" is better than "dwelling on it" until you get to a point where you can actually start fixing it.
In the medium term, start getting on therapy and medication and work on getting to a stable place - friends you like, job and living situation that you like well enough, etc. If you can have pets, pets are great - they will remind you that it's time to eat or sleep or go out, and they're great companions. My cat will try to physically herd me into bed if she thinks I'm up too late, and she's usually right.
Hope this helps and that everything starts looking better for you.
Look up the channel "Kitten Lady" on YouTube; she has a lot of really great tutorials on caring for newborn kittens and a few with advice on giving flea baths to kittens.
If you do give them a bath it's really important to keep them warm and make sure that they don't get cold when drying off. Fleas also cannot stand dish soap if you use that to bathe them (usually useful for making a ring around their necks to stop the fleas from swarming their head while the kitten's body is under water). Since they're SUPER newborn babies, I don't know if I would risk a bath just because they're so fragile with their temperature - I'd ask a vet there. But, with or without a bath, I think you should try your best to get as many fleas off as you can, maybe with a flea comb. They're so small that they don't have a lot of blood to lose so fleas can do more harm than you might think.