What could this mean?

This is the first time I'm using opk and I decided to continue testing even after I got a positive surge. It stayed positive until I ran out and then I took the pregnancy test but it was a BFN after 10dpo. I'm going to wait to test in about 4 days which is when AF is expected. I went to the bathroom today and checked my cm and it was light  Brown with light pink. Could this be implantation or the start of AF? Please share your thoughts. Thanks! I need positive vibes 😔