A viral cause can lead to refractory vomiting, and I agree with the testing thus far.
However, if it continues, you may want to consider more serious conditions, like gastroparesis, intussusseption, or other, bacterial-based, infections.
Obtaining further tests, including abdominal imaging, or an upper GI series, can be considered to look for these causes.
If there is a headache associated with the symptoms, a neurological cause can be evaluated for as well.
These options can be discussed with your child's personal physician.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin Pho, M.D.
KevinMD.com
Twitter.com/kevinmd
Correction Dr. He vomited on Friday and Saturday night around 7p.m. He did not vomit Sunday or Monday. Sorry for the confusion. He had been to swimming lessons the previous Monday and Tuesday also before the vomiting started