How do I know if I am bipolar?

How do I know if I am bipolar? I am a 20 year-old female college student. I have been bulimic for 4 years. I am 5'3" and my weight has varied in the past 2 years between 80-97lbs. My lowest weight a result of continual dieting combined with extremely heavy drinking, my highest weight a result of pure laziness and binge eating. I continue to use illicit drugs and alcohol, as a result of their abuse in the past, especially alcohol, I have lost several close friends, fought with my parents, been fired once for drunkenness, been sent to the hospital/psychiatric evaluation on two occasions, i've self-harmed for almost 8 years although it was not serious enough to leave scars until i started again 2 years ago. I've been quite a heavy smoker for around 5 years. I used to steal a lot, especially when drunk, I've stopped since I set off the alarms at Old Navy, although by some miracle I wasn't caught. I've had 17 sexual partners, I've contracted chlamydia, I cannot stop picking at my face and I grind my teeth very loudly in my sleep. My roommate moved out a few days ago because the environment in this apartment makes him 'not get anything done'. I am his only roommate. He's complained about how much weed I smoke, and I can tell he doesn't like mess or my friends or when I stay up or sleep on the couch. But doesn’t everyone feel manic sometimes? Also, I am a low achiever and not productive at all. I go to a good university but my grades have been getting worse for years. I’ve failed two classes since I’ve been here which apparently is some big deal. I just stopped going. How do I know if that’s bipolar disorder or just laziness?