Thank you for your question.
Any unprotected sex in young fertile women at any time in the cycle and especially around the time of ovulation is a risk for unwanted pregnancy. If you are within 72 hours of unprotected sex you can take the ipill as emergency contraception. Another alternative is the copper iud which is over 99% effective at preventing a pregnancy and also provides ongoing contraception. You will need to see your gynaecologist for this and also for advice about the combined pill which will prevent such an event in future.