What Causes Delay In Period Despite Having Safe Sex?

Hello doctor,My boyfriend and I had proteced safe sex on the 4th of January.. My periods were due on the 7th of January. We did use a condom, however during the act I suddenly felt really wet down in my vagina and for a second I thought the condom broke and it was maybe his fluid. I asked him if it broke, he said no it did not break. He said that it was my vaginal fluids only. He also said that he did not ejaculate while having sex. He had withdrawn his penis and then ejaculated outside, into the condom itself. He later on even checked if the condom had broken he said that there was no liquid oozing out of the condom and that the condom was intact. However the next day he mentioned that he realised that the condom that he had used actually expired about 2 weeks ago. I haven t got my periods till now..I m two days late and I m very worried. Also I m 18, and this was my first time. Should I be worried? Or am I overthinkinng?? There was once when I got my periods 3 days late.. But that was months ago and sometime I am a day late.. I also have an application called period calender that tracks my periods and predicts it and tells me about my pregnancy chances if it is high low or medium and for the 4th of January (the day we had sex) it said that my chances were low. But we had safe sex. I m really worried. What should I do?