What Causes Delayed Periods Along With Nausea?

Hi I had a sex with my bf .but we used protection bit don't know y .my last period was on 15november then till now their is no period. I m scared I tested trough prega news both the time it shows one single line..... In the C ...only ..if the single lines comes then m I pregnant ..even also I met a doc I just told them my periods are not came .so dey said take a tablets their is a Harmon's problem.and come after 10days.but now its been 6 days now m getting a vomiting after having tablets and all so I want to know m I pregnant