i think i have bipolar disorder

i am 15 and currently think that i am suffering from bi polar disorder. i have a lot of extreme ups and downs all the time, i will feel really happy and laughing all the time and then 30 minutes later feel extrelmly aggrevated and have a headache. i get mad at my friends for no reason and hate them more than anything. it affects a lot of my relationships b/c ill be in class one period and they'll see me all happy then try to talk to me the next class and i just dont want anything to do with them so they think that im mad at them and wont talk to me. this is and has been affecting my life for the last 3 years and i thought it was just mood swings at first but then in health class we were learning about mental disorders and bi polar disorder was one of them and i have most to all of the symptoms we went over. its kind of scaring me and taking a huge toll on my life. i dont know what to do about it because i am not close to my family and i cant open up about something that easily.
any suggestions on what i should do?? thanks