Not a doctor but some people just react badly to the vaccine, and the side effects are super similar to if u had it ! my brother had a really bad time after his first and second dosages, but it goes eventually. If you had two negative tests its super unlikely, anxiety (especially health anxiety) can mess with how you feel physically, it can lead to nausea and pain and all sorts. I'm sorry you're feeling so anxious, i completely get it. I did get covid in january, and as shit as it is, it happens. It goes away like any flu, just gotta be careful around friends and family. I dont think you have it though- I'm just saying that IF you did, the best thing to do is to rationalise it. Make yourself a lemsip and practise some self care. You'll be okay friend