First, congrats on your degree. It is a proof that you are like 80% of this forum: with problems but functional.
Who the hell told you that a degree will make you happy? * shock* Do you know someone whom a degree made happy? I don't. And I myself have a bunch of degrees and if they did something to my happiness, it is only decrease it.
So...
And in general.... you write about all that stuff: depression, mental health issues, self harming like it is a big special tragedy. It is not. It is pretty normal and common. You plain have somehow to live with that. And you proved with your degree that you totally can do it.
And a paragraph on happiness.
I have an absolute sure trick, how you can feel happy for a day. Everyone who tried it confirms. You certainly have a bicycle. Right? Choose a route between 200 and 250 km and ride it in one day. Then a day break and on third day ride it again. Somewhen on third day you will start to feel happy. Your butt will probably be shredded and you will be in physical pain but happy. It will also decline relatively fast. But.... I mean...