Thanks for your question.
You have severe stomach pain with vomiting so high probability you have any stomach pathology-most commonly peptic ulcer disease
,gastritis,may be pyloric stenosis
due to mass or ulcer in the pylorus and rarely due to hypertrophic obstructive cardiomyopathy(common in children),may be a stomach volvulus or atrophic gastritis
.So please do a upper GI endoscopy,barium xray and USG whole abdomen must and as early as possible .depending on the report you may need a biopsy if a mass is detected and then consult a gastrosurgeon or general surgeon
for his opinion.
Dr Sourav Ganguly