Irregular Periods & Pregnancy Symptoms: What to Know

Question
My girlfriend is 18 and only started having regular sex after we got together, which was just over two months ago. Since then her period has been screwed up; the last one was 8 days early, and had less discharge than usual, with less actual tissue, mostly just blood, with some brownish blood. She's also been experiencing other symptoms like her stomach hardening and her breasts being tender. She finished bleeding three days ago, and we're wondering if she could be pregnant even though there was bleeding. She took a pregnancy test and it was negative but it was on a day she was bleeding so we're wondering also if she was on her menstual cycle would it screw up the test... and how long now we should wait before trying another test.  

Answer
When was the first day of your girlfriend's last period? It does not matter if the period started 8 days early or was lighter than usual or brown rather than red. If she did get her period, she is not pregnant. If she has a 28 day cycle (from the first day of her period until the first day of the next period) ovulation occurs on cycle day #14. She can ONLY become pregnant if she has unprotected sex on cycle day #13, 14, 15, or 16. If she did become pregnant on one of those days, a pregnancy test would not show a positive result until 14-21 days after conception. The best time to take a pregnancy test is seven days after missing her period. A pregnancy test measures the presence of HCG (human chorionic gonadotropic hormone). If the hormone is present, the woman is pregnant. If the hormone is absent, the woman is not pregnant. The test measures the hormone whether she is bleeding or now. Nothing screws up the test. If she has not had her next period, wait another week and then take a pregnancy test. Make sure she keeps a record of here bleeding (date). It does not matter if it appears to have started earlier or later than usual or has more or less flow.