@Cats I'm so sorry you feel how you do.
I can relate almost exactly to what you describe - it's almost as though you were describing my history! Of course everyone and everyone's experience is different (even when they sound the same), but there are a few positives I can offer in the hope they might help a bit.
In my case I also had to do some digging into the past / my childhood. It wasn't easy and initially brought up more pain. However, in time, it definitely helped. So it did get worse, but then it got better (thank goodness!!). Hopefully the same happens for you.
I had also managed depression fairly successfully for many years on a certain medication - but then started to feel really crappy again. In my case, with my psychiatrist's support, a change in medication made a big difference. Of course I'm not advocating that for you - meds etc are entirely up to you and your psychiatrist / dr - I'm just saying there are changes / other options that might help.
The brilliant thing is you seem to have a great relationship with your psych - and I agree if you have that connection, having someone who knows you and your history is great. That way even when you haven't seen them for a while, they are well placed to help again.
Btw - going back to bringing old pain back to the surface - it's been explained to me (and I've read) that sometimes when we're younger we bury certain feelings, experiences (including trauma) or memories in order to cope with them. We might also develop certain self protection mechanisms / habits to try and stop that painful experience happening again (eg we might keep people at a safe distance so they can't hurt us). However, unfortunately the buried pain doesn't necessarily go away, and side effects of our coping mechanism (eg loneliness) might even add to it over time. If the 'buried pain' gets too big it can resurface (some say when we're strong enough to deal with it). That can make us go from travelling along ok, to all of a sudden feeling like crap (without us knowing why).
In order to ease the resurfacing pain it might be necessary to revisit the initial cause. This can make us feel even worse initially. Particularly because our brain can make revisiting the initial pain feel like we're going through it all over again. Yuk! However, addressing the initial cause (and perhaps learning to let go of our coping mechanism) can help us feel better. Ideally even better than before the intial pain resurfaced (fingers crossed!!).
The 'buried pain' is a bit like a beach ball we're holding under the water. Initially we can keep it under and everything seems fine on the surface. However, as it keeps inflating, holding it under gets harder and harder. Eventually it pops out of the water - causing pain (seemingly from nowhere). Plus we're exhausted from trying to keep it under. So we might feel like crap and have no energy. To feel better we need to examine the beach ball - which hurts even more - but is the only way to find the valve, open it, and let the air out.
PS - I also had long periods off work. It sucks, but if that's what you need to get better, try to give yourself that permission. It might be frustrating etc (and financially challenging), but pushing yourself too hard too soon might mean more time off in the long run. Taking the time you and your Doctor think you need might lead to a fuller recovery and a smoother more permanent return to work when the time is right.
I hope some of this helps.
Sending support and best wishes,
GTT