I'm confused. Are you saying this problem went away when you stopped going to school due to covid? If that's so, did you eat differently? And if not, does being at school make you nervous?
Headoyle, I sympathize because I've had similar problems in the past! In my case it turned out to be certain foods & food additives I can't tolerate. Things that can cause these symptoms: Milk or anything with added lactose; any sweetener that ends with "tol" such as sorbitol, xylitol, mannitol; saccharine; anything with inulin or chicory root. Those are the big ones for me. I've learned the hard way that I have to read the labels of EVERYTHING I put in my mouth. I can't even chew gum that has xylitol! Another possibility you might consider is gluten intolerance. Irritable bowel syndrome is another possibility. Please keep us posted, I really hope you can solve this issue!