It was a couple of years ago, so I can't remember verbatim how it was explained, but it turned out the intense bleeding that I was having was 'breakthrough' bleeding. Which sounds benign seeing as much as I was bleeding at the time.
Essentially, the hormone levels were not strong enough for me anymore, which might have had to do with me getting older and out of puberty, I don't really know.
It's wierd, and I was pretty angry about it at the time, because I also, didn't think that BC could just stop, but according the my gyno, it did.