You should definitely talk to someone about this, probably the school counsellor or some other kind of counsellor. If you don't know of any, ask your doctor.
Try not to worry too much about it being bipolar. A lot of people think that bipolar is just having mood swings, but it's not, although of course mood is part of it. If mood swings are your only problem right now then it's probably not bipolar. Some teenagers go through periods of bad mood swings just as part of being a teenager. But if it's bad enough that it's really impeding you, you should talk to a counsellor about it who can help you control it. And if you have a counsellor monitoring you they can tell if you ever do develop other problems that might mean you do indeed have a disorder.
Be wary of anti-depressants. People can develop bipolar later in life if they go on anti-depressants too early in life, including young teens. It's part of the reason why America has just a higher rate of bipolar than other countries.
if you need someone to talk to, it doesn't make you a burden. im not sure what your thinking about, but maybe its something so hard to think about you get depressed and then mad that something happened? lol just a guess. but seriously if you need someone to talk to go see a psyciatrist or therapist. if your bipolar you could maybe go on meds or for depression, if your not someone who hates taking medicine for things like that.