Thank you for your question.
Having sex after four years can cause one to have bleeding, which is most likely normal and as a result of injury
inside your vagina.
However having said that, if you do not have a yearly pap smear
you should have one done because one of the cause of bleeding after sex is precancer or cancer of the cervix
which needs to be ruled out by doing regular or yearly pap smears. If your previous pap smears have been normal and you have been having them regularly then I would not worry a great deal and I would expect that your bleeding should stop in due course of time as the area heals up properly.