take an hpt if your period is late. if it's negative make an appointment with your ob/gyn for an appointment there could be something medically wrong that needs attention.
I imagine that amount of vigorous exercise might be enough to disrupt your hormones, but if I were you, I'd get a home pregnancy test as soon as possible to be sure. Sometimes light spotting like that can signal implantation of a pregnancy. I've been pregnant a few times, but unfortunately only miscarried. But the color of the blood around that time for a couple of days was pinkish. (I've also heard it can be brownish.) Good luck! I hope it works out best for you!
If you've been having unprotected sex, you could be. Why not take a pregnancy test?