Three week hell

So basically I get the worst periods it starts and it goes for a week. Then takes a four day break. Then I get it again for up to three weeks. I went on birth control to try and solve my constant period. It's been a year all the birth control has done is delay it for a few months and then it comes back. Currently on my third week of period. I am 15 and I've had my period  since I was 13. Not sure what to do.