How bad does your period have to be before they will put you on birth control?

First of all I am 15 and NOT planning on having this is not something I'm trying to do so I can have . I wouldn't say my periods a terribly painfull I mean I have a few here and there that are really bad the only thing is I have a bad leg pain and minor cramps but only lasts for the first day but they are really long like 8-10 days. Is this normal? How bad does your period have to be before they put you on birth control