Thank goodness I am not the only person that started thier period that early! I have never before heard of anyone else! I don't know how old you are but until I was 20 I had very heavy periods. I would wear a super tampon and a super pad plus a super pad sideways front and back at night. I would still wake up with a mess all over the bed! I told my mom and i guess it didn't rejister because to this day she doesn't remember being told. She was horified! Well I am 34 now and I guess I out grew that part of it but I still have erratic periods. Some times way to much them barely anything. I always wondered if it something to do with starting so young?... I don't know.
Also I have a thyriod problem and one time I kept getting normal results but didn't feel right. Well I went to a different doc. who used a different lab and I got help. I was told that not every lab reads thier results exactly the same and there is a range of numbers for normal. As long as you are in the range they will say it's fine. But sometimes our body needs to be at the high end of normal to function right. Don't know if that is what iron works like to but worth a try. Good luck
Bye the way, I've tested negative for anemia too, time and time again. I had a psychiatrist look at me in shock, like he saw a ghost. His demeanor changed and became very serious, when he said, "you need to take an iron pill with your period!" I told him my bloodwork being negative. He basically said screw the bloodwork and take the iron pill. I had had symptoms for years, including heavy periods, not quite as bad as yours, but still HEAVY. I don't know why but I decided to take it for the week before my period too. Within three months I started taking it daily. My period is now NORMAL. I mean normal!!! I knocked a day off it, cut flow by at least 25%, and no more clots, which had been extremely large. I've been on it daily for 2 years now. My iron is still normal.
You might want to investigate Hughes Disease too.