Vomiting - 21 month old boy. This be?

10days back, my 21 month old boy suddenly vomited while playing. He felt very sick post that. N vomited everything he ate. I gave him Gastica n he was better. He had fever that night but morning he was fine. Today, he suddenly vomited again after waking up from his noon nap. Vomited thrice since then( the last vomit being yellow) n gelt uncomfortable; rejecting food and makes a face to puke if fed still. The only symptom that remained in the last 10 days, which probably I shouldn't have ignored is, he said no to food and would gag at the sight of food. Have given Gastica n entrrogermina. Have given some khichdi as well. Hoping him to feel better. What could this be? Anything to be worried about. He doesn't have an upset stomach.