I want to go on birth control because of my period

My periods are 7 days, I am soooo heavy and I get the worst non stop cramps. It also makes me feel so sad and fatigued all the time. I cry all the time. I’m 15 and I have no one I can talk to about wanting to go on birth control. But how much does it cost?? And is it true you can only take it for 10 years?