AF was due 11/24,only 7DPO

I'm 7DPO (Had a + opk CD 8 & 9,had ovulation pain CD 9) I had sex with my boyfriend today and then I started cramping and bleeding,I'm pretty sure I started my period,it's painful physically and mentally 💔 Especially after my miscarriage in July 😢 I'm just not understanding why did it start so early? 7DPO? I did nothing different this month,I'm relaxed.