Hi CG. Your post is very well-written. You do description well. I pretty much had a flashback to last winter, which was just the lowest point of a pretty bad four years.
In my case, I started going to psychotherapy and had a meds change and I almost suddenly got much, much better. One reason for that was greatly improved sleep.
How is your sleep? If you have a device that can download apps, I would recommend one called SleepBot. I first heard of it from another poster on this forum. It monitors your movement and breathing/snoring while you're sleeping and creates charts that let you look at how often you're coming out of restful sleep. Or, if you're like me last winter, you may be not sleeping at all for large parts of the night.
The med that was added that helped me so much was low-dose mirtazapine/Remeron at 7.5-15 mg. Besides helping my sleep, I have lots more energy and my motivation is greatly improved.
I think usually when someone reaches a plateau like you've described, their doc changes their main antidepressant. For me, that's Cymbalta. I need it for fibromyalgia pain, though, so that's why my doc didn't change it.
I hope you'll let us know in this forum how things are going for you. I would urge you to tell your prescribing doctor all the things you've said in this post about feeling like you're in a fog, lethargy, losing your ability to enjoy things that you previously enjoyed, and the frequent suicidal thoughts and urges to self-harm. Maybe you already did - if so, say it again! These are some serious indicators that you need a medication change.
I'm not sure if you see a psychotherapist. If that option is available to you, I'd urge you to take it. It can be hard to do when you're feeling so down, but sharing what you've expressed here with a mental health professional besides your doctor is important.
Hugs.