hey, i'm 18 and the same thing happened to me when i was 16.
yes the blood loss is making you tired you most likely are anemic and need to go to the doctor. you'll probally
get transferred to the hospital to have a blood transfusion. I let my period go on a lot longer than you did before i said anything. It wasn't a very good idea. I don't wanna freak you out but i was dieing cause i basically didn't have any blood and no iron in that blood. I went to the gyno and they put me on birth control to regulate it and it works fine.
So please go to the doctor, i don't want the same thing to happen to you,