I need advice from someone who's been there (depression in high school)?

I have been suffering from depression ever since I started high school. I have exactly one friend, and she's not in any of my classes so I'm alone alot (I'm not what you'd call "popular"). I just feel so empty with this numbing sadness and loneliness and the only thing that keeps me going is the fact that in two and a half years I'll be out. But the days just seem to drag so much and I'm not sure I can make it. Any advice from someone who's been there?