Girlfriend goin on 4 days late?

Me and my girlfriend had un-protected sex like 4 days before ovulation period. We stopped completely before finishing. She said her last period was a little weird she didnt bleed as much so she thinks she is pregnant from last month when we did it a day after ovulation of the previous period. Shes had been stressed a bit latley and more physically active way more then usual so i think it could be that. But goin on 4 days and no sign of her period coming she thinks she pregnant. What are your opinions on this? And please refrain from going on about precum and it containing sperm. Im a believer that pre *** doesnt contain sperm because there have been tests that testify against that. And i did nothing for sperm to be in the urethra to be flushed out with it. Note shes been off her birth control for round a few months she said so she thinks it could be from where her period hasnt been naturaly happening from that and shes having abnormal periods last late she had was like 2-3 months ago and it was 1 day late.