Please what could be the cause of irritation and then vomiting after eating?

Hard to know, but...: The GI tract has very limited # of symptoms to signal its distress--nausea/vomiting, diarrhea/constipation, bloating, pain, fullness, bleeding, etc. As you know, many of these characterize ibs, but are also seen with inflammatory, infectious, ischemic, malabsorptive, & functional disorders. Directed lab work & imaging are appropriate. For now, stop NSAID's, alcohol, smoking, & start acid blocker.