I was thinking that it might be helpful if you could get something in writing from a daycare he was kicked out of, for the pediatrician. The daycare professional would have an objective assessment, and might provide the pediatrician with some clues, a direction to pursue. What did the daycare person observe, what did they try, why did they make the decision to end his daycare with them? Explain that it's for a medical assessment and ask for their insight.
In the meantime, before the pediatrician's appointment, document as much as you can. If there's a particularly bad incident, document everything that was taking place before the incident (food, environment, noise, time, etc). Keep a food log, and be specific.
And do NOT be embarrassed. This is a worrisome situation. You wouldn't be embarrassed to seek help if your child had a fever of 104. Asking for help is good and loving parenting. Sometimes a child is easy to raise, and sometimes they can be a challenge. It's ok to say that you need help.