Academia isn't for everyone! I've not been in your situation, but I have been in the situation where I had dropped out of education due to poor mental health (midway through the second year of my degree, after a previous false start at a different uni) and found myself at the age of 22 with no formal qualifications beyond my A-levels, in the depths of depression and thinking myself a huge failure who'd disappointed everyone.
The good news, relatively speaking, is that it was a huge wake-up call to me that I needed to devote time to getting myself mentally healthy and figuring out what it was I really wanted out of life. If your depression is telling you you're a failure, that doesn't invalidate your feelings, but it's an indication that it's not a good thing to be listening to - I mean, if it was someone you knew telling you those things, would you want to stick around them? I'd hope you'd want to kick them out of your life, or at least get to a point where you could say "No, you're wrong."
I'm a firm believer that no one is categorically a failure - they're just judging themselves according to the wrong criteria. Maybe university isn't for you. Maybe it is, but not right now. In that sense, if you're only 20, time is on your side. If you don't feel up to working, have a look at volunteering opportunities, which are far more flexible; you might not be earning money, but it's a good way of trying out different things in a low-pressure environment. (I started out in archaeology and ended up enrolling on a nursing course for this year at the ripe old age of 26, which is a pretty good example of how volunteering can completely change your idea of what you'll end up doing!)
As an aside, if your medication isn't helping, it isn't the end of the line - medication is by no means a precise science, and what works for one person rarely works the same way for the next. I took four different meds before I arrived at my current combination (like you, I'm dealing with depression and anxiety, which can be a tricky mix to medicate), which sounds alarming and time-consuming, but trust me when I say it's worth it when you reach the right balance. And once that happens, you may find that you get a sense of a fresh start and a new direction.