How is this possible 😱 how did I get pregnant

I had unprotected sex with ejaculation inside me 2 days before my period. (13th of October) Period came (15th of October, ended 18th)

And THEN I just got this feeling come over my body and decided to test. ALL POSITIVE (29th of October)

Huuuuuh??? But how. I got my period for that month?? Doesn’t that mean I couldn’t of conceived?? And also wouldn’t I of been past ovulation the night I had sex? So many questions

*edit* my period came on time actually. Was very heavy and normal. Seemed like the real deal