Depression...Bi-Polar?

I'm kind of thinking that I possibly have bipolar disorder...I go through stages of being very hyper and happy...and others I am very down. Lately I have been more down than usual. I don't have thoughts of suicide, but I wish I didn't feel so low. There really isn't any reason for my depression, or even my mania. I'm not soo keen on the idea of brining it up to my parents, because I usually pretend to be happy around them, to avoid questioning since I don't have many answers...I don't know what to do...Help? Please...