Hi, welcome to the forum,
vomiting and nausea can be a sign of infection of stomach known as gastroenteritis (often with diarrhea and vomiting), lactose intolerance (difficulty digesting the lactose in milk), indigestion, gas formation, obstruction etc.
As you are vomiting you need to maintain water and electrolyte balance. Anti emetic, antibiotics, antispasmodics will help reduce symptoms against prescription.