Light red bleeding and pinching/cramping 4dpo 🤔

Hello! So, me and my husband have been ttc for almost 3 years. My cycles are pretty normal, but I have never experienced this before. I know exactly when I ovulated because I use opks. Around 2dpo I started having these pinching sensations in my uterus, and then cramping this morning. Went to restroom to see I had some bright red bleeding as if I were about to start aunt flow..... I have no idea why this is happening. It’s too early for IB, and waaay to early for my period. Has this ever happened to anyone? I am still having some bright red spotting and mild-moderate cramping. I also have sensitive nipples... Any thoughts?