Depression does hit people about your age. Some in high school and others in college. It's hard, but it's not just about finding who we are. Since the changes in your life have lasted MORE than a few weeks, and people are starting to notice, that's when I would talk with a professional. If you are in the U.S. then go to your college counceling center (sometimes it's free), if else where, then ask someone around your school.

It sounds more like depression then just find out who you are. But that's my opinion.