Spotting implantation vs period


Hi. So I am totally confused. I was supposed to get af today (5/9) but a really light pink spotting showed up on Sunday (5/6). Since then I have had really light brown discharge that doesn't fill up a whole tampon and is inconsistent. Today af is supposed to show but it's more of the same I took a test and it's bfn. I am always on time to the day, but this is weird. My lower back has also been hurting and my nipples are sensitive. Has anyone experienced this? Is this just another trick from af or is this possibly something more?