Can I get pregnant at 23 after unprotected sex?

Hello doctor,

I am 23 years old and have been experiencing irregular menstrual cycles for the past six months. At the start of this month, I had unprotected sex but took a contraceptive within 72 hours. My period arrived on the expected date, but for the past three days, I have been dealing with nausea, body pains, and weakness. I am concerned about the possibility of pregnancy despite taking the contraceptive and having my period. I have had a history of a six-month irregular menstrual cycle, and earlier this year, About two years ago, I had similar symptoms related to delayed menstruation. Can you provide insight into whether these symptoms might indicate pregnancy or are linked to my irregular menstrual cycle? Kindly help.

Thank you.