Misdee, I think your situation is 'special'. You have to deal with some really rough stuff, and it doesn't go away. Have you really had a chance to recover? It's quite possible that, when the stresses you are under ease a bit, you will find that you have the opportunity to recover fully.
Certainly, in my case, I believe that my depression did eventually get better completely, due to a life-changing event. I had PND after my first child was born, and, although I had techniclly recovered, I always felt 'in remission' rather than 'well', but when my second child turned one I realised that I had not relapsed into PND. Yes, I'd had blue spells, but never as bad as PND. Finally I felt 'well' again.
But while I was in that knackering first 6m or so of 2nd-time-around-motherhood, when you don't know whether you're coming or going, I often agonised about whether I was succumbing again, and felt that I wasn't moving forward at all. So, TBH, I don't see how you could either. What you have to deal with is so much harder. You are amazing to be coping, and eventually you will get the opportunity to rest and recover fully yourself.