I'm not a doctor so I can't say that you don't have depression. In my opinion, you have just developed bad habits. It's definitely easier said than done, but you must do all you can do break those habits. Motivation is the key to breaking bad habits, in order to garner that motivation try reading some quotes. Replace the bad habits with good ones, for example, if you feel like staying up late playing games, read a book instead. When you go back to school, hit up the gym in the morning and before you leave campus. It's not going to be easy, but keep in mind, nothing of value comes without hard work.
Here is a link to a post about quotes.
motivating-quotes-vt870.html