Ladies, why did this happen?

I was nearly 10 or 11 days behind schedule for my mensuration. My fiancé and I had sex two days ago. I cramped up for about 30 minutes afterwards. And two or three hours later I was bleeding. It wasn't my normal flow, and it was a very light pinkish color. It was off an on for a day. Yesterday at 7pm it just up and stopped.
I took a pregnancy test too see, and it came back negative. I have no idea what or why this is. Any advice?
by the way I live in a small town and have no obgyn here. So I'd be driving about 70 miles round trip.
Ladies, why did this happen?
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