I had period for about 8-12 days now and I'm still a heavy bleeder

I'm 14 and I'm NOT sexually active and this has never happened to me ever when I'm on my period and literally I never had my period for along time I had it for about 8-12 days now and I'm still a heavy bleeder cause usually I'm always a 5 day period but I haven't had my period in 2 months and this month I finally got it back and I'm bleeding big clots of discharge blood that's black I told my mom and my skin has been looking a bit yellow and I much dizzier than ever I'm really scared can some one help interpret my problem but If no one has a clue I'm going to a lady doctor on Monday