Having sex during your period lowers the pregnancy risk but doesn't rule it out completely, since sperm can survive for a few days and ovulation timing isn't always predictable. Since you're unsure whether ejaculation happened inside and you don't want a pregnancy now, it's reasonable to consider emergency contraception as a precaution.
Next Steps
An emergency contraceptive pill from a pharmacy works best within 72 hours of the unprotected sex, and it's more effective the sooner you take it. If your next period is delayed by more than a week, take a home
pregnancy test to confirm.
Health Tips
Emergency contraception isn't meant for regular use and can affect your next cycle's timing. Please see a gynaecologist to discuss a reliable ongoing contraception option.