Fighting depression is a full-time job! I would know.
Start with a good diet routine. Avoid alcohol, sugar, soda, chocolate, and those "energy" drinks. Stick to meat, vegetables, fresh fruit, lots of water, and coffee if you can tolerate it. I don't recommend fruit juice - lots of calories, sugar rush and then crash. Not much better than soda.
Exercise if you can. If you can't afford a gym, then take a good long walk. Whatever you can do will help your mood.
If your depression is persistent, see a doctor. Medication can help. Some OTC supplements can help too, but I can't recommend any of them, since they haven't worked for me yet.
Get up early and go to bed at a reasonable time. Take a one-hour nap after lunch if you need to.
Avoid negative people. Tell your parents that you understand why they're upset, but you need them to be supportive. You need to walk out into the world with a smile on your face if you're going to find a new job.
Don't beat yourself up over losing your old job. Everybody makes stupid mistakes and even honest mistakes. Don't be too picky about your next job. It's just a stepping stone to your dream job anyway. You could try temporary jobs or volunteer work, as long as it keeps you busy and relatively happy.
You seem to have a computer. Chat with people online when you're lonely. There are health sites that discuss depression, which is a serious disease, not a mood you can just snap out ot.