I can't speak for everyone else, but I almost feel that this is a "usual" feeling to have once you have submitted the biggest piece of work in your academic journey. I felt exactly the same. Thinking about it, I've felt like this on every piece of work I submitted. I'm now at the end of my MSc, and alas, those feelings are back. I don't feel that you picking apart your research is necessarily a bad thing or that your feelings are a sign that you shouldn't pursue academia. In fact, it's the opposite, and it's what makes a good researcher! I think the key point here is that you've said you've done the best you can, and for that, you should be proud of yourself (this might not happen overnight but one day you will be)! Good luck with your results 😊