I am on the patch. i had sex one week ago today, my period was due yesterday and hasnt arrived, is it likely that im pregnant or just that my period is late?

Pregnancy unlikely: In a woman with regular periods, some causes of a late period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (like birth control pills), hormonal imbalances, etc… That said, pregnancy is still a common cause of a missed period if sexually active. Home urine pregnancy tests are very accurate by 3 weeks after sex.