Me and my girl friend had sex about 3 weeks ago. I did not ejaculate but pre-ejaculate. And it was not even inside of her. She gets her period once ever two months. I mean if she gets period on the first week of August, she gets next on the last week of September. So she nomaly skips a month. But after we had sex and after like 5 days, she got her period which is not usual. Can it be a possible sign of pregnancy? She doesn't experience the other symptoms yet though. Please help