Is this being bi-polar?

Ok, like my moods change REALLY fast. I can be extremely nice to someone one minute and hate thier guts the next. I just get so annoyed and fed up with them! For example, I'm sitting here in a chair by the fireplace on here. My brother got a phone call and I said, "Was that cy?" And he said, "Na, she probably won't call me back for about 15 minutes." and I said, "Oh, ok." Then he walks over he to me being all nice and says, "Watcha looking at?" and I said, "It's none of your freakin business my God! Go away, you get on my freaking nerves." and I just started yelling at him. And I do this to everyone! And I can't help it. I just get so annoyed with them; it feels like I just hate them at that point. Then sometimes I'll be happy then five minutes later I'll just think of something and start crying and be all sad. My mom is like this too. Why do I do this?