My Period Is Supposed To Come On The 25th Of

My period is supposed to come on the 25th of December, my last period was on the 25th of November and they usually last for 4-5 days. I recently had sex on December 17, and be been scared lately and overthinking that I'm going to be pregnant. My boobs have been sore lately, I don't know it's because my period is about to come or something else, I don't feel nausea or anything i feel perfectly fine. I'm 16 years old and my mom doesn't know that I lost my virginity I don't want to tell her now because she will be disappointed, I need help please