Hi,
First of all, sperm can live in the female genital tract for up to five days. So if you had sex on the 11th, there certainly could have been viable sperm still in your system to be there to fertilize your ovulation on the 16th. Furthermore, modern
pregnancy tests are extremely sensitive, and can become positive even 10 days after conception.
However, if the test is not performed correctly, or if the test is left out too long beyond the time recommended to read the test on the package, a faint line can appear.
So at this time, I recommend waiting for your menstrual period, and if it does not arrive on time I would repeat the pregnancy test at that point. At this time this has should give you an easy to see, accurate answer. But it is certainly possible that you could have conceived this cycle.
I hope I was able to adequately answer your question today, and I hope this information was helpful to you. Best of luck in conceiving.
Regards,
Dr. Brown