Do you know what is bleeding? Does it come from the vulva, the mouth of the vagina or inside the vagina?
If you still have an intact hymen or partly intact hymen, tearing it can cause bleeding.
A little bleeding is not great cause for concern. If it happens every time or very often, or it is heavy or won't stop there can be problems that should be looked at by your doctor.
Little bleeding can be caused by small cuts and lacerations, from intense contractions to the cervix and uterus during orgasm or from infections in the vagina.