I wrote this in another post under pregnancy section...
Some woman can bleed during pregnancy I did with both light/medium bleeding it was worse after sex but that is somewhat normal depending on the circumstances..
Anyways as long as your not hemmoraging, bleeding that fills more than one pad an hour or have severe cramping/they told yout the baby is fine with no complications then, its completely normal..
I will not say it your perfectly fine because I dont know your whole story but I do recommend you see a dr, now if you have a u/s and baby looks fine, your placenta is fine then your one of those people like me who just bleed during pregnancy...
Stress can also cause you to bleed but unfortuantly being preggo brings tons of worries that does make you stressed just relax, I have two kids with whom I bleed with both are healthy each one being over 7lbs.