Bleeding after sex?

Has anyone bled a little after sex but then not anymore after? I have Monday once and today once and it's light pink/brown. I'm on birth control but I often wonder if I am pregnant. I got pregnant on birth control earlier this year but sadly it ended in a miscarriage. MY period isn't due for another week or so and I wonder could it be implantation bleeding. But why only during sex? Any help would be appreciated!