I get angry and fantasize about hurting people I'm woundering if my mothers bipolar is just now showing up I'm 13 so now would be the time...

No, bipolar problems don't usually show up until the late teens or early twenties. And bipolar doesn't manifest itself as rage and hurting people.

Have you gone to an anger management class?

No I haven't

I don't show emotions to people so I thought it was just my way of showing it (to myself)

So how does your rage manifest (show) itself if no one can see it?