I Think I'm Bipolar...?

Ohk so, it started off by my one friend always calling me bipolar. But she jokes around a lot. But really, when I thought about...maybe she was right. I'm either uber happy and cheerful or depressed or agitated. Not that I've been diagnosed with depression, it's just what I feel like. And then, another one of my friends told me she thought I was. And she isn't the joking type. She said I act on impulses. So now I'm just kinda wondering, could it be true? Last night I got in a fight with the first friend but now I feel so stupid about it... It truly was my fault for acting so grumpy. But I totally blamed her for being so touchy... So, do you think I'm bipolar? And if you don't know can you tell me any information on it and how people get diagnosed? Really, I don't know too much about. All the sites I visited on it weren't very good. Thank you so much. :)