My Son Is 18, Never Sick, But 72 Hrs Ago

My son is 18, never sick, but 72 hrs ago just started feeling sick. His upper abdomen hurts, feels very full after only two pieces of bread or a small container of yougurt, feels nauseated but has not thrown up, has shortness of breath after eating, has fatigue, but no other symptoms. His pain is a 5 up to a 6, the pain wakes him up at night, no diarrhea, stool is normal, urine is normal, no sore throat, nothing else at all. Has not traveled, has not been exposed to anyone, is still in high school, 12 grade, but did eat mushrooms 48 hours before feeling sick that we think may have been bad. Also he feels maybe his cat may have given him a parasite since the cat stays outside all day. It comes in at night and sleeps with him. Any ideas?