I had sex on July 20th, and I was scared out of my mind that I might be pergnant due to pre cum, but I took a test yesterday on August 8 and the test came back as negative . I just want to know what could be some other reasons why my period has not popped up yet. I asked the dude I had intercourse with and he said that for some odd reason girls start their period a week or so late when he had sex with them . He says he don't know what it is but it just happens.. Any suggestions . btw iam going to the doctor soon to be sure