Why am I most likely spotting? 😩

I am on CD17, 4 days since + opk, and I *think* 3DPO (possibly 4DPO because I think I caught the end of my LH surge with my opk). My cycles are usually 28-30 days. Tonight my husband and I had sex (nothing rough or anything, no pain) and when I went to the bathroom right afterwards a noticed some blood. It was light pink and not a lot. But there was definitely blood. So what gives? It’s way too early for my period but also too early for implantation unless I ovulated before my positive opk. So confused.