What Causes Vaginal Bleeding, Mood Swings And Headache After Having Unprotected Sex?

Hi, Me and my boyfriend had intercourse last Saturday without protection and I have been moody and sick with the stuffy noise headache and fever . I took two pregnancy test , and they where both negative but now I have bleeding lightly the following Saturday after . I normal have irregular period but they always start off heavy . Is it possible I could have implantation bleeding or my period is just stalling?