So you've been depressed for months or years... and no matter what you tried, you hover on the bottom with a few periods of somewhat better times.
There is no one answer to why YOU are stuck in the vicious cycle but chances are, it falls into one or more of the below categories.
You may have a genetic disposition to depression (I wrote about this before). Truthfully, if you have it, then depression will always be a part of your life. BUT, it is not a reason to always feel bad or give up on having a relatively peaceful mental state. However, you need to look at it as a condition like any other (like ADD, diabetes, whatever) that you can manage. So, shift your mindset from curing to managing!
You've tried therapy, medication, behavioral changes (good or damaging), mind over matter tactics, coping mechanisms, self-medication, environmental and social changes, and everything you could think of... but nothing gave permanent relief. Why? Because your efforts focused on relieving/eliminating depression rather than the state of well being. I didn't get this for a long time (more precisely, 40 years). There is a huge difference between lessening depression and increasing wellness. Consider this: 'I'll eat chocolate to subdue depression symptoms' versus 'I'll eat chocolate to increase my energy'. The act is the same but you tell yourself a completely different story. So, change the narrative from depression focus to wellness focus!
You have too many habits that feed the depression cycle. Most of us start out with coping which turn into habits in as little time as a month. The problem is that we become so comfortable with these habits that we do them unconsciously and defend them when challenged. If you ever heard yourself saying 'but it (snacking, watching YouTube, avoiding chores, etc.) helps me feel less depressed' then you have pervasive habits. Often these habits are reinforced by fear of change, maintaining comfort (enduring the known suffering is perceived less trouble than questioning it), simple unawareness of unsupportive habits, active defense of the habits, and a variety of reasoning and emotional attachment to habits. So, get real with habits and replace the outdated ones with new ones!
Spend a little time to figure out which of these factors drive your depression cycle and start changing them one step at a time. Do something every day to reinforce the change. It is a slow process but getting on the path of healing starts with one tiny act.
Love and healing to all of you!