Also, as another commenter said, professional help is gold. If you have access to it. If you don't, then you should explore ways to get such access. I dealt with debilitating depression in the past, and ended up getting care from government-run facilities. They were excellent.
It was extremely clear what my triggers were. The sustained changes of mood were very clearly visibly graphed and the blurbs, even with almost no effort at all applied to writing them (many were just: "ok day"), made it very clear what the inflection points were.
I was very surprised just how much the results of a single day can change the subjective day to day experience for weeks without being consciously aware of the single days happenings that caused the change.
Some people have been helped by things like changes in diet.
YMMV and personal professional supervision should always be sought for serious matters.