I'm sorry you're going through this, but just to make it clear, the emergency room is for taking care of an urgent, immediate situation at hand. They are not there to diagnose what may be long-term physical ailments. They provide care and refer you back to your regular physician.
I've broken bones and they x-ray, tell me the bone is broken. Give me crutches or a splint, pain medication and refer me to someone else for the follow up.
Emergency room doctors are just that. They treat emergencies. They make sure a patient is stable enough to go home or they have them admitted to the hospital.
I don't mean to sound glib. I really don't. If your child's oxygen saturation levels are normal and he has unspecified abdominal pain, ruling out appendicitis etc, the ER will send him back to his regular doctor.
That said, my son started vomitting. I thought he had the flu. He vomitted at night and then was fine by morning. He had no fever. He didn't really want to eat which I thought was normal after throwing up, but after four days, only throwing up at night, I took him to the doctor.
Turns out it was acid reflux and the doctor prescribed a medication for him.
The vomitting stopped immediately.
I didn't allow him to eat after a certain time in the evening, I propped him up so his head was elevated. He took medication an hour before his last meal of the day and it was like a miracle.
He no longer takes the medication and we just have adhered to the cut off for eating if he feels his stomach hurting, he sleeps slightly elevated.
Your son may be having a reflux of some kind. It really burns. My son, however, only complained about feeling like he was going to choke. Then the vomitting.
The good news is they have ruled things out.
I just want to say that at a thousand dollars a crack, I wouldn't rely on the ER to give you answers or a diagnosis. They aren't primary care physicians. You'd think for a thousand bucks, it should cover every test available, but it just doesn't work like that.
Follow up with your pediatrician or better yet, get a second opinion.
When my son was diagnosed with his reflux issue, I couldn't get him in to the pediatrician and took him to see my doctor who knew exactly what the problem was.
I changed it so my doctor was my son's primary care physician after that even though he didn't specialize in children.
If you aren't getting answers the route you're going....try a different one.
Best wishes.
I hope your son will be feeling better soon.