Hi, I had gone through your question and understand your concerns. Well if pregnancy test was positive then it is very likely that you are pregnant and this bleeding was probably implantational bleeding, not menstruation. Less common this may be sign of spontaneous abortion. This is true especially if you had one risky intercourse s you said. To be sure you should do pregnancy test which can be done when period is missed or 8 days after the targeted intercourse so at this point it would be accurate enough to detect possible pregnancy. Standard urine test would be enough for it since this is almost 99% accurate. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions. Wishing you good health.