i had sex with my girlfriend but her period came earlier than expected. 5 days after sex

If her actual period came 5 days after you had sex then she wouldn't be pregnant if it was just light spotting then she could be.

If your not using protection when having sex then there is a 50/50 chance of pregnancy happening! If you both don't know how the female cycle works and when is the safer time to have unprotected sex you shouldn't be having sex yet!