It suddenly stopped?? Help!

Hi all! I have PCOS so I take Birth Control that's 3 full weeks of actual birth control and a full week of placebo pills to give my body time to have a period. I'm four days into my placebo pills, and about a week ago I took it like 6 hours late. Last night i actually started my period, it started as it always does with some dark spotting. I had sex with my boyfriend just after I started my period last night (he didn't finish inside me, he never does, and this time I didn't finish at all). This morning I woke up and I haven't had a period all day, it seems to have suddenly stopped. Did having sex mess up my period? Could I be pregnant? HELP!!