Our daughter who is 18mon. now has been doing the same thing since she was a year old. It doesn't matter what kind of food or drink it is and always happens when she is eating. She will cough a few times and we can sometimes get her to take a drink and that will stop it, but that usually doesn't work. She will heave a few times and then be perfectly fine immediately after vomiting and will want to eat again.
This is so unpredictable we can't do a swallow study. It usually happens at home or when she is eating or drinking in the car. I don't recall it happening at a restaurant or at anybody else's house. She can go weeks between vomiting episodes.
She did have reflux as a baby but we have been off that medication since before she turned one. She does not appear to be nauseous or have heartburn, constipation or diarrhea.
The pediatrician has given her Zofram, but I don't think she is nauseous because she eats. She tested negative for celiac disease. I really don't know what to do either. Maybe she is eating too much, I have no idea. My husband and I think it may be related to the reflux she suffered as a baby.