From your questions it is not evident on which day of cycle you had sex. That is important for a precise reply. Emergency pills sometimes alter the existing menstrual cycles. It is actually a higher dose of hormone, so it can have it's effects on endometrium and this spotting is a frequent symptom. There are tests which can indicate the possibility of a pregnancy
but it is prudent to wait to your next expected date and then do a urine pregnancy test. We see a high failure rate for emergency pills.