Diarrhea after possible implantation?

20 DPO, 8 days past what I believe could have been implantation bleeding. (Very light pink CM, then one wipe of very light pink blood. I used a light days tampon and when I took it out it was only maybe 25% saturated with rust brown blood. Absolutely no bleeding since then.) My period is now 6 days late but tests are still negative. Since that little bit of blood I have had lower back pain, a come-and-go dull ache mostly in my right breast, and diarrhea. Has anyone experienced this before? Am I getting my hopes up? I read that a lot of women, especially those with PCOS like me, take a lot longer to show a bfp, sometimes as long as 4 weeks. Edit: The spotting happen ed 13 DPO, but because of my PCOS I'm not totally sure when I actually ovulated. Could have been later.