What Causes Delayed Period While HPT Is Negative?

Hi good day doctors, im 2months delayed i wonder if i'm pregnant or what? I took a PT twice but the results are negative. The first day of my last period was Nov. 23, 2014. My husband and i make a sexual contact last dec. 11 and it' s a withdrawal,. And i expected that i will have my period before 23rd, but i don't have period ,. And we do sexual contact again 4th week of dec. And its withdrawal again , so meaning to say my husband ejaculate inside me twice, is it okay?