Sometimes you can spot if you have sex right after having your period or from birth control
but it could easily be something else too
if it happens again, I would go to the doctor.

I'm on seasonal and I was spotting for two weeks and the gyno checked for cysts (but I was really spotting cuz I didn't take it the same time every day) so i'm thinknig that spotting can be a symptom of cysts!!