I know its of no help to you, but I'm just out the back of a BAD 6 months of this, and a moderate to middling 12 months before that.
4 things I found helped me:
1) Vitamin D supplements. Placebo, or a decent help - fuck knows
2) Exercise - I started using my turbo trainer and just jumped on it 45 minutes every now and then with some shit on Netflix as a timer. However everyone's fitness level is different and even just a 15 minute stroll could do wonders
3) Cutting down the drink. I do still drink, but not every other night like I was. Tricky to stick to, especially after a soul crushing day, but has definitely helped
4) Saying "fuck it". Yeah that fucking dense cunt has just cut me up and didn't even realise we would have crashed if I didn't brake. Yeah the boss is chewing me out for something way out of my control. Yes this doddering fucker in front of me is weaving all over the place at 1mph in the supermarket so I cant get past them.... Fuck it. What does it matter to me in the long term? Fuck all. I'll have forgotten about it in 10 minutes, and I 'm going to make a conscious decision to not let it ruin my day.
Took me a good 18 months to turn things around and can now see a bit of sky through the clouds. It is absolute shit, and feels like a permanent dark, foggy cloud hanging over everything you do.
I feel like everyone is tested at times, and everyone's tolerance to it is different. My own experience tells me it goes in peaks and troughs, but does get better if you hang in there, and gets better a bit quicker if you can force yourself into making some positive changes.
Again, everyone is different and I wouldn't want to prejudge your circumstances or project on you, but I reckon you can hammer through it and get back on the level.