I think i may have bipolar disorder?

I am 17 1/2 and for the past couple of years (besides being a typical teen) i have experienced a series of highs and lows both rapidly and over a period of time. I can be very happy to manic, then suddenly i can barely get myself out if bed. I have attempted suicide several times and consider it everytime im depressed, which can last for a number of days. My mood changes very dramatically and i have no medium. My problem is, my parents wont listen due to religion. They think i am just listening to my feelings. How can i be diagnosed and get help?