Help. I don't know what happened

Marissa • USN
One day in class I had my first migraine ever. Part of my vision was lost for a couple minutes. I went home and used the restroom and wiped and saw blood. It's was lighter than period blood and I had a period about 7 days before. However the "period" was brown and a little weird and not normal. It wasn't just a little blood when I wiped, I was filled up the whole wad of toilet paper. 
Then me and my fiancé were having sex and he pulled out saying something was wrong. At first I thought it may be a yeast infection because I was having severe yeast infections the last month or so. Then when I went the the bathroom in the middle of sex, I wiped and saw blood again. Not as much though, and I wiped again and there was more. And it was like fresh blood, not dark period blood. Almost pinkish looking. 
What is this? I'm afraid I had a misscarriage but never saw a little body. But is this what it is or could be? 
6 weeks before this happened, he filled me up. It was during my fertile window but I took a plan b. Did the plan b not work? Or is this a sexually transmitted disease possibly that is causing this? I had no symptoms but anxiety, migraine, and dizziness