Early Period & Pregnancy: What to Know After Sex

Question
Me and my girlfriend had sex on a saturday and that next wednesday was supposed to be her period, but her peiod came earlier by 1 day.  Is she pregnant?  She also started the pill on tuesday, the day her peiod came.  She said you can't be pregnant and still have your period, but is it possible to have your period and be pregant, even if your period comes 3 days after having sex.  It was on time, her period I mean.  

Answer
A woman cannot be pregnant and also have her period. If she got her period, she is not pregnant. Also, if she has a normal 28 day cycle (from the first day of her period until the first day of her next period) ovulation occurs on cycle day #14. She can only become pregnant on cycle day #13, 14, 15, or 16. She cannot become pregnant on any other day of the month. She cannot become pregnant four days before starting her period. If she does become pregnant on one of the days I mentioned, she will miss her next period and a pregnancy test taken a week after she misses her period will be positive. Once she is on the pill, her chances of becoming pregnant drop to less than 1%. Don't worry.