Menstruation cycle problem. On track?

Hello Doc, I've got menstruation cycle problem. The monthly cycle date keeps shifting ahead every  month. But it never gets delayed for a month or two. I had my last period in the month of September around 14-15. It lasts for 5 days. I don't know what possible reason could be for this as I was on a vacation from May to first week of October and then college started so stress couldn't be the reason. Maybe me not doing any chores or physical activity could be. I tried eating papaya three days back. Generally, after having papaya I used to get periods within a day or two, but this time it's taking longer. Also, I've started exercising since last month. Is it something serious to worry about? And what should I do to get my menstrual cycle back on track? Thanks.