Brownish spotting 9 days before AF expected?

I have pcos and my cycles can be somewhat irregular. Last cycle was very late so I started taking vitex and AF came almost immediately after starting it. I've continued to take it and glow predicted my ovulation to be on 5/16. I also started metformin three days ago.

Just now I noticed some brownish discharge? I've been having some cramping and sore breasts which I don't usually have before my period so I don't know.

Implantation bleeding is usually pink/red, right?

Thanks for any input. ❤