Some advice please? :)

So recently I decided it was time to shift a little bit of weight and today I went for my first jog/power walk for about 45 minutes. When I was almost done I felt a bit of dampness like I had just peed myself a little and when I got home I found it was blood. My period isn't due for a little over a week and in 13 years I have never been early or experienced spotting inbetween periods... could it have something to do with exercise? Any experience/ advice would be appreciated!