At a loss

I’m so confused. I thought I knew how pregnancy, ttc, ovulation, etc worked pretty darn well. The life throws me a curveball! My period was supposed to start Saturday. Saturday night i started have this weird nauseous feeling. Every single day since then I have had the same feeling off and on, mostly in the afternoons or evening and worse when I don’t eat much for more than 2 hours. I have taken a couple tests, and had one vvvvvvvfl that could barely be seen at all. When I took a test this morning it was totally negative though! Could I still be pregnant? It’s possible I ovulated late, like around the 17th of November. I just need an explanation! Thanks 🙏🏼