What Causes A Delayed Menstrual Period With Negative Pregnancy Test?

sir i have done sex with my Boy friend on around 27 jan but that was not done properly and in that month i have my period at 13 jan around i dont even remember that 13 was the starting date or finishing and in the month of feb i have taken around 3 tablets of ovral g in 9,10, 11 feb and till today i dont have my periods around two day back i have done prega news test one pink line appear saying negative but i am getting worried .