4 yr old, severe stomach cramping some vomiting. blood test, urine test and ultrasound came back ok. symptoms started a week ago. what could this be.

Viral: Moat illnesses like this are viral in nature and can last a week to ten days. Other considerations are abdominal migraine, food allergy. The blood test and urine ruled out serious infection and urinary infection. Ultrasound ruled out any obstructive process. If it continues then see your doc again.If nothing improving a visit ot eh gastrointestinal specialist could be helpful.

Yes, but....: Most illnesses which cause vomiting in children are viral, as stated in the previous answer. This should be gone in a week to ten days. If it persists, it could indicate a food intolerance. Vomiting without an apparent cause lasting more than a couple of weeks needs to be investigated, including for the remote possibility of a brain tumor, since irritation of the medulla causes vomiting.