How do you know if you have insomnia?

I don't sleep for about 2 nights in a row and then I will sleep for maybe 6 hours and then not sleep again... And when I do sleep I wake up throughout it! I have been really irritable and my moods have really been strange! I'm tired for a lil then I get huge engery boosts then I am tired again.... I don't know what to do any advice?