Do I have night time depression?

Hi, my name is Leanna, I am going into the seventh grade. When I was about four my parents got a divorce. My biological mother is addicted to pain pills, and anti-depression pills, and the reaction of all of them put together gives her tremendous headaches, but she thinks she's got some sort of disease, so she sleeps all day, basically everyday. My Dad got remarried when I was five, and that gave me: one stepmom (of course), two blood brothers,and three step brothers. My stepmom was more of a mom to me then my own mother. In nov. 2007, my dad ped away, and my stepmom got custody of me. (like I said, I don't think she's an evil stepmother or anything.) I now have a five year old half brother. During April of 2009, we started looking for houses to move. I felt sad because I'd lived in the same house my whole life, and that was the last place I saw my father. At school I made straight A's, and I was very bubbly. But when I got home, all I really did was sit in my room and listen to music. We finally moved, and then a couple weeks later my stepmom got a boyfriend. They've been together for only three weeks, but I don''t really like the idea of it. I want her to be happy, which is why I feel I'm in an emotional battle with myself only because it's uncomfortable for me to see her with a man that is not my dad. at night all I do is sit in my room, but again, during the day I'm fine. at night I'm bored and lonley, even with a houseful of family. I start my new school in six days, and I'm nervous about that too. I'm worried about myself, because both my grandfather and my biological mother have bipolar dissorder, and I don't want to live an un-happy life. Do I have a mild case? Please help!