As you have posted the same question in 3 forums (2 under the heading of "Confused"), I have copied and pasted my reply to you in the other forums:-
Do you keep a menstrual cycle chart so that you know when your periods are due?
It could be that this was the time for your period to start.
If it is nowhere near the time that your period was due and you get this every time that you have sex, then make an appointment with your doctor to get checked out.
Best wishes.
Bleeding during or after sexual intercourse depends on your menstrual status,tightness of the vagina where non lubrication increases friction,friction causes irritation and rupture of mucosa (this is not heavy bleeding). First time intercourse (virgins) some times have bleeding and have painful penetration but it varies from person to person.How old are you and how long have you been sexually active.
Dyspareunia(pain during sexual intercourse) associated with bleeding may suggests mostly menstruation status but other conditions like UTI,Vaginal diseases of different origin should be eliminated if you have this problem haunting you for a long time.
Observe for two to three days to see if the bleeding subsides or there is any vaginal spotting.Symptoms like fever,aggravating recurrent pain in abdomen,back pain requires medical attention.Talk to your doctor and undergo pelvic/per vaginal examination ( only after bleeding subsides),and get evaluated accordingly.Update your status and come up with more questions if you have any,if this information does not clear all your doubts.