Bleeding between period & ovulation?

So yesterday was exactly one week since my period ended, and I have 5 more days before my fertile window. However yesterday, I had a ton of cramping, back pain, and even had some small amounts of blood when I wiped, along with thicker CM. I'm really confused why I had any blood or cramping/pain at such an odd time? Any opinions? My last period was very heavy by the way, so there is no chance that I was pregnant, because I tested negative all the way up until AF. Then had a heavy period, and have only had sex 2 times since period ended a week ago