Why was your son absent from school on May 20 and 21?
He came home from the band competition and complained that his stomach hurt. The next day he felt worse. I took his temperature and found that he had a fever, so I kept him home. I think he has food poisoning. You should check out the restaurant that they went to.
I suppose it could be food poisoning. Symptoms of food poisoning usually appear in the next day or two after eating contaminated food.