has this happened to anyone before???

So I'm on the pill, I took all of them on time and didn't miss any. I had unprotected sex at least 4 times within the last month and my guy came inside me 2 of those times. My period came on time, it was mostly that brown starter period late on Wednesday, Thursday it was pretty heavy all day, Friday it was a lot lighter, like barely half the tampon was full after having it in for a few hours. Saturday there would only be about a quarter size amount on the tampons all day. And then it seemed as if my period ended. (My periods are normally 4 days). Today is Sunday and I started my next pack of pills today, but it seems like my period is starting back? I have this kind of cramping on my right side & the blood looked a bit orangish-red, what could this be??