my periods are 2 weeks late but the pregnancy test is negative even when I'm feeling pregnant

I had unprotected sex with my boyfriend on the 17th and 20th November. I normally get my periods on the 26, 27 or 28 of each month. This time my periods never showed up. I did 3 pregnancy tests and they all came out negative. I thought maybe I had tested too early as it was before the two weeks wait. I then went to see a doctor yesterday, this is now 16 days after intercourse and two weeks with missed periods and the pregnancy test came out negative again. I did not do the Sonar and the blood test. Im feeling all pregnant and I have most of the symptoms. Can I really be pregnant even if the pregnancy tests were all negative? I just want to be sure about this.... Im a bit confused. What do I have to do now?