Hello,
I need to ask you a question. You said you don’t have a support. Neither you count with the possibility to do therapy and attend to see a psychiatrist or psychologist to treat that depression? Because it would be a great help, meds and therapy could help you to get a little bit out of this hole.
You sound pretty much like me when I was younger. That sense of isolation and catastrophic thinking, easily drowned by any mistake even when it could be only considered a obstacle.

Yes, you sound very hard on yourself. You already got an A in one of the tests and this is something to consider as very positive but I know you can only see now the negative.