Are you seeing someone who can give you a hand with this? A counselor or psychiatrist, or even your GP? Some of this depression can be controlled by medication and therapy.
I know the feeling you have of things getting better and then *wham* it all goes down hill again. I used to live in dread, waiting for the other shoe to fall, or the *wham* to hit and the spiral down into depression again.
All I can suggest is that, until you can get help, focus on one day at a time. Ask yourself if you can get through today, just today. At one point during my teens I focused on getting through to lunch, then getting through to dinner, then bedtime (which was my favorite time of day). I couldn't even focusing on making it through the who day. So that is an option, too.
Meanwhile, keep posting and we'll help you get through the days.