What Causes Spotting After Been Hit On Stomach?

2 nights ago I got held down in a fight, the person shoved me down by putting their elbow into my stomach and did not get off me for a couple of minutes. It realy hurt at the time and is still sore although I don t have a bruise there. I have spotting, starting about an hour or two after it happened. I have a regular cycle and am not due till next week and I am on the pill.