Strange emotional changes every 2-3 months?

Hello,

I've tried searching google, and asking some friends, but no one seems to have any idea whats up with me. Once in a while, usually every 2-3 months, I get into this very strange mood.

The mood changes only happen for about an hour or two, but in that time I can be happy, sad, angry, lonely, confused, laughing hysterically, you name it. And the mood can change within 30 seconds of one another. I feel like everyone just kind of piles up at once and my brain explodes. I've tried searching the internet and come up with a few possible things but nothing conclusive. I've had an anxiety attack once before and know what that feels like, and this isn't it. Any help would be greatly appreciated.