Unprotected sex and came inside of her a week ago but bleeding this morning what is the cause to that? did not believe that periods are capable of happening while pregnant

Periods : Periods are not normal during pregnancy. If the person in question is pregnant and she bleed after sex then she needs to see her OB doctor right away. On the other hand, if you had unprotected sex (and she's not pregnant) and she bled a week later, then you can assume this is her normal period and she did not get pregnant from your encounter; however if the bleeding is mild/spotting only then she could very well be pregnant and she can take a early prediction pregnancy test 6-7 days before her missed period.