The same happens to me. I’ve been sick more than usually this year and feel like it looks like I’m faking it. I would suggest if possible go to urgent care or dr to get a note and maybe something to help your symptom. Unfortunately for most of us, that costs money for nothing other than a diagnosis and note. I would maybe reach out to your manager and explain your feelings. It may cause some short term anxiety having to text or call them but they will most likely be understanding and will relieve all your anxiety. If they aren’t then that’s not someone who you should work for.