Welcome, Aquarius anon! Your story struck a chord with me. No one can know your specific pain but many here have felt that darkness and that lost feeling. I (and we) will always welcome any discussion that may help you find what you search. keep digging, and searching, and never stop. You are stronger than you know.
I feel compelled to share a bit of my personal journey in a hope that it helps you in some way. It is not the same as yours, but I do understand that feeling you describe. My whole heart goes out to you!
I am recovering from Depression and GAD as a result of Complex PTSD. Unfortunately, I was not diagnosed properly for far to long which allowed issues to get serious. The feeling of being lost, feeling like things are getting better and then getting knocked right back down, not knowing how to get back to what you feel you can be, the crushing feeling that keeps you in bed. Those words are deeply familiar even though your circumstances are different.
Many people will not understand your situation, but there are people that have gone through them and people that can and will help. You are doing the right thing… you are searching. Keep going, there is something, somewhere that will help you take a step. That step will lead to another and another.
If you get knocked back down, don't lose hope. This is a process and there is not a single silver bullet.
Spirituality was a major component of my healing. It became a cornerstone, but there was a lot of other foundational corrections required. Be patient, don't beat yourself up, and know that you will be stronger for this challenge.
I wouldn't wish my journey on another living soul, but I would not trade it for anything. I have come out with tools and perspectives that many won't ever need or have. I have found several people along my journey that I have been able to empathize with and help in there journey. This I view as a great gift.
Through all the darkness and pain, what were you supposed to learn? At some point, you will be able to turn this experience into a strength. Keep an eye on that, use that as a beacon, and keep going!
May you be Happy. May you be Healthy. May you be Free from Undo Suffering. May you find Peace.
Eye am Keeping an Eye on you! <Big Internet Hug>