Are you in first year? I'm second year law at Oxford and had entirely the same crisis in the final term of first year but I refused to drop out because Oxford has always been my dream uni, but last year I was fighting to drag myself out of bed and study a few hours a day because I hated being here so much. This year I'm enjoying it way more, feeling way more motivated and my grades are higher but nothing has really changed except my outlook on my degree. Give it time and you might find things just naturally improve. For a lot of Oxbridge students it's a massive shock to go from being top of your class/constantly receiving academic validation to suddenly just being average (because you're now only around people who were also top of their class)