Implantation or AF?

Grace
I was one day late on my AF this month. Then I THOUGHT I started but it seemed different, it was a lot lighter and it was just spotting. So confused! I took a hpt this morning and it was negative :(. The last time we had sex was beginning of August & he pulled out but I do remember it being during my fertile week just not sure exactly what day bc I forgot to log! Any thoughts??