I'd like to start off by saying that there is a 0% chance that I am pregnant. I have had very regular periods up until now. I had started my period on the 7th of Sept and it was normal as usual, lasted 7 days. On the 18-20 I started spotting enough that I had to wear a liner. My next period was due on the 5th or Oct and it still hasn't made an appearance. Just after I had started my period on the 7th of Sept, I started brisk walking 30 mins twice a day. Before this I was not active very much. Is it possible that this new exercise routine could be causing my period to be irregular?