I'm not sure if I have depression. Help?

In the past four years, my parents have gotten divorced, both have met someone else and gotten remarried, both of them have moved, I got four step siblings (two on each side), and a half brother. I go back and forth between their houses with my younger brother who has aspergers and bipolar. I feel very responsible for him.Depression runs in my family. Around the time my parents separated, I started getting sick a lot. I missed about a day of school a week and spent the rest of the time at school with my head on my desk.In middle school I was considered pretty quiet.I get migraines frequently. I've never really been in a relationship because I will like the person one minute but the next be too emotionally exhausted to care what they thought about me. I get panic attacks (mostly in math class) and I missed a lot of school days just because I didn't feel like I could get out of bed. i just told my mom that I was sick. I've had a lot of problems with my neck and back. Sometimes I just don't feel like doing anything, like I'm just totally drained even if I haven't done anything. I don't like being around large groups of people for a long time because I feel like taking a nap afterwards. I'll laugh and joke but for the most part I don't feel really happy. It differs from day to day, though. One day I'll feel awful and the next I might feel fine. What do you think?