What Causes Persistent Diarrhea With Odor And Vomiting?

my son has had diarrhea for two days and finally vomited this evening. He is 10 and just got off an antibiotic for what they thought may have been strep throat. His diarrhea has had a horrible sick smell, but his throw-up smell was like nothing I ve ever smelled....like YEAST. He did have subway yesterday (I thought he was better...we had energy and wanted to eat.....he pooped through the night.) Nothing is staying in him long. Though again, he only just threw-up. Is this the stomach flu or with that smell should I take him to an urgent care?