Problems at School and Home?

I'm sixteen years old and lately I've been having trouble at school. For the past two years in high school, I've been getting straight As and generally been okay at home. But since of the start of the school year in September, my grades have been steadily dropping and I've been getting into arguements with my parents all the time. Although I've had trouble making friends in high school and don't really have a best friend or even a close friend right now, I've never felt so depressed and I cry myself to sleep a few times a week - is there something wrong with me? Am I just going through a "bad phase"?