i often get a few days spotting, then a day or two break then a few heavy days before calming down to spotting then stopping again, it can often spread out over ten days or so. I know for me this is ok as there is no chance of pregnancy since my partner passed away years ago and i have stayed faithful to him since.
you have a certain amount of blood and lining to loose every period, so if you spend days just spotting, then it is logical that it will take longer than the usual week to empty your body of the whole period. think of it like two bottles, one has a pin prick hole that the water drips out of, the other has a large hole so the water pours out of it, which one empties the quickest?.. the one that pours out...it is the same with your body, the heavier your period the quicker it is over!