What is it about and what should I do if my period is late?

Hello Recently my boyfriend and I had sex. He, of course, had a condom and before ejaculation pulled the penis out of the vagina and came "outside", I will add that the intercourse was recently and a week earlier and the case with ejaculation was the same. Now, about 10 days after the last intercourse, I have enlarged breasts, which meant that the period was approaching, but for 4 days it was late. What is it about and what to do? Best regards