Pregnancy related question Urgent.

I am 26 years old and currently 7 weeks and 2 days pregnant. I got my period last on 5th of November 2017. I have a very little pcos but not in a medication level. My doctor said it's common in pcos to get pregnant or to have ovulation without a visible period which happend to me i believe. Because i didn't have any period on December. According to my ultrasound scan, my lmp is 17th or 18th of december. My period normally stay upto 6 days. I have a 32 to 33 days of cycle (But it happend to me twice or thrice in my life time that i got my period within 29 days). Now my question is that i had unprotected intercourse on 24th of december and later on 2nd and 3rd January 2018. So which day did i conceive??? It's very important for me to know. Please help me with it.