period question

My periods are 100% regular. They start they day they are suppose too and end the day they are suppose too. In July I got pregnant and MC the beginning of September. I got my first cycle in October and it lasted as long as it was suppose too. My AF was due 10/31 and it came on the day it was suppose to (that bitch) it was a heavy period but it only lasted 2 1/2 days. It always last 5 days. Any insight on why I had a short period??