Long Period HELP!?

Sydney
I am currently 17 and have had my period since the day after I turned 10. And for the first it was a little irregular, but ever since I turned 11 it been 4-5 every month, and I get really bad cramps 2 days prior, well this month, it's been really weird.. I have been on my period for 21 days. Just wondering if any of you have experienced this! Thanks!!