New here! Not really sure…

Hi, I’m new here only had this app for over a week. I had my period last week which finished on the 13th. According to app I am at my highest today and tomorrow for fertile days, I ovulate on Saturday. But before my period I did a test because I’d missed quite a lot of pills, negative. But today i started feeling really nauseous, I don’t feel ill or anything. Is this me just overthinking, because surely it’s not possible to be pregnant yet…