I use to wear unprescribed contacts, leave them sometimes over night etc..
Sometimes i'd wake up to my eye very pink when i wore them over night, but i stopped wearing them for a few years now. Since i wore contacts, it seems my eyes always wake up with yellow/green stuff in the corners. I've had discoloration around my entire eye since as well, could this be something serious?

First, don't mess around with contacts that aren't prescribed. It's good that you've stopped wearing them. Second, it's hard to say much about the green stuff and discoloration. Go to an optometrist and get it checked out if you're worried about it.