AF was 11 days late but only lasted for a day?


This cycle has me thoroughly confused. I was 11 days late for AF when she came Sunday morning. Sunday was light bleeding and really only noticeable when I wiped. I apologize if this is tmi, but my flow was very watery light pink with some clear cm. Today (Monday) it has tapered off. I was 21 dpo when AF arrived and was testing BFN as recent as Saturday. I doubt it's implantation bleeding, considering it's three weeks past my ovulation. I had never been late for a period before...anyone else have a similar experience?