I'm sorry you're finding things so difficult, it certainly seems like a lot and many people would struggle in your situation. Will the surgery be allowing you to speak to another doctor? Could you even change doctors for good if that's possible? It's scary when a doctor makes a mistake and I know it can be hard to trust them again. Is there a pharmacist you can talk to about the med in the meantime?
I'm glad your manager is trying to support you as best as she can. Would it help to talk to her more regularly about how things are? I'm sorry you beat yourself up for your mistakes, it sounds like there is a lot of pressure on you which makes you bound to make some mistakes but we all make mistakes anyway. What is it you worry about when you take time off work, that you might not make it back? Could you make some kind of plan with your manager to test the water with time off and see how it goes? Or is there something within the workplace she can do to make things a bit more manageable for you?
That must be extra hard changing your living situation just before lockdown. Are you still in contact with people at least? What's making sleeping hard for you?
That is really awful with the lack of support. Are there any charities who would help you since I think some places offer emergency support to people who are struggling to access CMHT support etc. There might be a helpline you can call, which I know isn't really good enough.
I know how difficult it can be to focus on things and then how difficult it can be to continue with them. Are there any things that feel ok that you could do? You could give yourself a break from the mundane things for a while. What do you do when you're feeling distracted? Do you skip from one activity to the next, just sit and do nothing, or what? I find that trying to force myself to stick with one small thing for more than X minutes which would be my usual lack of focus time can help to keep your mind on the task.
I hope you at least don't feel so alone here. Please keep posting if it helps.