What could this be?? Mid-cycle bleeding

So the husband and I had unprotected intercouse around the time of ovulation. We're not really trying for a baby, but it was the heat of the moment sort of thing. My period isn't due until July 1st And the last two days I've been cramping and have been spotting. At first I (TMI sorry) had a think brown blotch of CM now just light pink discharge. What could the cause of this be?