Hi, Sam. I'm sorry you are feeling sad. When I'm feeling sad or even slightly down I make sure I get some exercise, preferably outdoors, eat as healthy as I can & definitely, like LaMa, don't dwell on the things I just cannot change. I think most of us have had or still have a tendency to overeat or eat the wrong things when we get down, but that just makes us feel worse & doesn't fix anything.
You have not gone back to being 17:8 & that is good. Are you able to talk to someone about feeling down & maybe get some counselling? It helped me a lot about 10 years ago. My self-esteem was very low, even after losing my excess weight & seeing a counsellor really helped put things into perspective.
Typing in your diary regularly might help a little in the meantime.