Hi fred4761, welcome.
I'm sorry you've been struggling with fatigue and nausea. Have you seen a GP about this if you don't mind me asking?
It could be anxiety. As Mark said, he feels sick from anxiety all the time, so do I, it's definitely common. Feeling like you have knots and butterflies in your stomach. That's perfectly normal.
I hope you feel better soon, and can see a GP to discuss these things and get to the bottom of it.
We're here for you, best of luck. I hope the nausea and fatigue subsides.