Sorry to hear that you are going through a rough time.

I would be cautious in trying to self-diagnose, and see a professional about your concerns. Depression alone can cause crying episodes, it does not necessarily indicate Bipolar Disorder. Can you talk to a psychiatrist, a therapist or even a GP? It could very well be school-related stress and if you are in high school, then there are also hormonal mood swings to think about as well.