Thanks for all the advice. One of my biggest problems is that I can't tolerate any ADs at all - have tried 8 or 9 different ones from different classes, and all make me suicidally depressed within days. I am also seriously testosterone deficient, but after a week on that I was again suicidally depressed. My cortisol level was checked a few months ago and it was normal, so that one seems to be a dead end too.
All this is why I say I feel like there's just something wrong with my brain that means that nothing works the way it should. There's clearly some missing piece of the jigsaw at the moment. The only things that work to blast the anxiety and depression out of my system are cold water swimming, and really strenuous exercise. So this morning at 9am I was swimming in the River Dart in the rain, not most people's idea of a relaxing Sunday morning, but it transformed my mood from yesterday when I literally couldn't get out of bed. And I have a rigorous program of Kundalini yoga (much harder work than any yoga I've done before) and Zumba classes during the week. I know it's all good for my health in general, but it's bloody knackering having to do this stuff just to keep going, and I wish there was more understanding of how the brain works so that I didn't have to put in so much effort just to have a half normal life.