Re: menstrual spotting after strenuous exercise
This could come under the heading of TMI. And I'm likely older than you. Some very light spotting after orgasm often happens but stops quite quickly. So maybe vigorous exercise can do the same thing? That's one thing. The other is runners often get blood in their urine after hard runs and that is attributed to the walls of the bladder slapping together during runs especially if its empty. So are you sure its uterine blood and not from your urethra/bladder.
Otherwise I have no suggestions.