What I'm thinking is that the main issue has been missed so far...: having to work.
You've tried so much and nothing's able to prevent the pain from overdoing it coming up, because it can't. There won't be any meds for that inside the next 10-20 years, research has a long way to go, as you know.
The only way for anyone to get pain from overdoing it down is to do less.
So for me the question appears to me how you can adapt your work or swap it. To help there we'd need to know roughly what is involved mentally, physically, hours, co-operation of colleagues and bosses, possibilities to apply for supplementing disability pay or reduction of hours...
Trying to put myself in your place by comparing with mine (in italics):
Your pain is 6-8 most days and it seems without meds a little more? (Or how do you mean "don't help"?)
I guess my scale's different: For me that'd mean my colleagues and my wife would send for an ambulance, because it'd mean I'd be crying and moaning all day (and I'm a tough guy).
I work 10h/w online, and could do 20-25h/w if necessary / possible without stress without overdoing it. However I'd then have less time for self-care and research. Before getting jab-triggered MCAS I was able to go to work for 1-3h/d, under certain conditions, plus about 5h/w online, pain of 3-5. 1-3h of rest after, pain of 2(-3). When I tried to go to work more, even online with stress more, my pain went up more and more to 5-6(-7), resting to get it down no longer helped, which meant worse insomnia, nothing helping, most (amitripytline, melatonin, CBD and supps) zombifying me, so absolutely impossible to work with no brain.
So readjusting my scale again, to "just about able to work without more insomnia and crashing". The result would mean I wouldn't be able to do anything other than work. I would have no life: I'd like you lose my partner (not now, but in your position), have no hobbies that involved moving, couldn't socialize at all, nothing I could spend my money on apart from rent, food and getting to work. I would ask myself: Is this worth it? As it is, all of that is minimized, but I can be mentally active all the time while resting (incl. stretching etc.)
Bottom line: For me it's important to make sure I have the right work-life-balance. Whenever that's unclear to me I talk with my psychologist about it. It'll have been different in your relationship, but I'd rather sleep on the streets than lose my wife. Less dramatic: I'd rather have "no" money than be unable to play half an hour of table tennis a day.
Next: What progression can you expect? Many med, esp. these, esp. pain killers, only suppress, they don't heal, so while I continue overdoing it, I'm exploiting my body. Which is what I actually did (not even needing meds) before my full flare crash, which brought me from 50h/w down to 0 for 10 months.
Fibro does not progress, but if we don't stop overdoing it, the symptoms will likely get worse and worse.
I'm not saying that'll happen to everyone / you, cos everyone's different.
But what are the chances, what risks are we taking when we overdo it, are they worth it and sensible?
Instead, my decision was to do what's best for my body, so work at self-caring, treatments and research. I think that's the only chance to get a better handle on it - getting out of the vicious circle, coming to rest, learning the sweet spots and limits, then building up more treatments to slowly get up again in a healthy way and maybe even reach much of the previous way of life without meds....
So trying to transfer your symptoms and their progression to your situation:
Considering how unlikely it is that your pain will get better, how likely that it could get worse:
Is this the best work-life-balance you could wish for?
Meds: Alternatives apart how might you try to adapt the meds?
I'm unsure how much exactly they're helping you.
On the one hand 'not much' and 'short term', 'back to square one'.
On the other when you them all, it was worse.
So first, how much less pain reduction do you actually get by the meds?
If your pain now is 6-8, does that mean with meds it's +1 or +2?
Comparison:
Apparently they'll helping you more than they did me: They don't help my fibro pain but increase other pains like skin and gut. If I were pressured to work and meds would decrease the pain a little, I would still crash big time, like I did.
Now if you add or increase a med and it helps short-term, but then stops helping:
What happens then: do you continue with it, or do you stop it because it stops helping?
If you need to continue taking it, because otherwise the pain will get worse again, it sounds like a spiral.
A possibility you may need to take into account is that a pain mechanism in your body may be causing this and will never let it end, it will always win. Our pain is notorious for being resistant to pain. Surprising that meds help you at all...
The only way out of that would be to stop working, wean off of all of them, and learn new pain strategies which may include maybe the same treatments that don't work when you're overdoing it and on meds, or try some new ones that your body doesn't know yet. That way your body might be able to work up positively and constructively into a different channel using all the energy you've been putting into work, rest and pain etc.
Regarding your previous med strategy of adding and adding, my idea would be to try slowly weaning off the one you feel is helping least and seeing how far you can go without symptoms getting worse. Is that a new possibility or did you try it like that?
BTW: With amitriptyline I'm surprised you're taking as much as 125mg. For fibro the normal amount is 10mg or 25mg, at most 50mg. Anything above would normally mean for severe depression. I do know people who take more, and it does seem to help a few, but I'm wondering what would happen if you tried weaning down that one?