I'm sorry to hear your son is going through this. I have not heard of abdominal migraines but wanted to share my story with you. My son had something called intassusception which is a type of intestinal blockage. He was younger than your son, only 10 months when it occurred, but the condition is most common in boys ages 3 months to 3 years. His signs were similar to your son's: random vomiting without any associated diarrhea, fever, runny nose, etc. He did tend to be a little constipated and had foul smelling gas. His episodes, as we called them, would come on pretty quick and could last for about 3 hours. He would writhe in pain and then throw up. Between bouts he would be pretty lethargic. The final MD we saw finally ordered an abdominal ultrasound and that was what we needed for a diagnosis. I don't know if any of this sounds like what your son is going through but it may be worth mentioning if it continues. Good luck and I hope you have some resolution soon.