whats the difference between bpd and bipolar disorder and how do you know if you have it?

what's the difference between borderline personality disorder and biplolar disorder? I feel like I may have one of the two but I'm not sure the difference and also if I'm just overthinking my situation. I could be so happy one second but then the next its like I hate everyone and everything. I could be perfectly fine but then I get overwhelmed with this feeling of anger or sadness and it could last from a couple hours to a couple days. I know this isnt normal but my parents refuse to bring me to get help so I have to rely on people on the internet instead, but I hate self diagnosing. somebody please help.